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根据短文内容，从短文后所给的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。
Texting(发信息)may be preferred over phone calling by many young people, but too much text messaging may increase the risk of neck or shoulder pain, a new study shows．
Judith Gold, an assistant professor of epidemiology(流行病)at Temple University's College of Health Professions and Social Work, presented evidence at this year's meeting of the American Public Health Association, saying that college students texted more, and they reported more pain in their necks and shoulders．She says in a news report that most people aged 18 to 21 prefer texting rather than email or phone calls． 1 “What we've seen so far is very similar to what we see with office workers who've spent most of their time at a computer,”Gold says．“The way the body is positioned for texting－firmly fixed shoulders and back with rapidly moving fingers－is similar to the position for typing on a computer．”
“ 2 It's the age group that texts the most, so it's important to know what the health effects may be to learn whether it will cause long-term damage,”she says in a news report．
Gold and colleagues conducted a study of 138 college students to see if relations exist between the number of text messages sent per day and pain in the upper body．They used body maps for the students to indicate areas of discomfort． 3 The number of text messages is so big that they were surprised at it．
The researchers say they found an association, only in male participants, between shoulder discomfort and the number of messages sent． 4
Why would texting cause pain in the neck and shoulder rather than the wrists and arms?“We were really surprised at this, too,”Gold tells WebMD．“Remember, this is just a beginning study． 5 ”
A．They find that males might be easily influenced by physical discomfort related to texting．
B．The students were asked how many text messages they sent per day．
C．That can possibly put the younger generation at increased risk for overuse injuries．
D．Further research needs to be done to confirm the results．
E．Texting has become a major form of communication．
F．Looking around our campus, you can see many students on their cell phones, typing away．
G．This is true only in female participants．
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根据短文内容，从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。
Whenever you are using the computer, your eyes are hard at work．Be kind to them by positioning the monitor 18 to 20 inches away from your face． 1
Position the screen at your eye level, with the top of the monitor itself level with your forehead．This will keep you from having to lean your neck back or forward to see the monitor． 2 They can help you raise the monitor a little higher by putting a few books under it．They can also raise the height of the chair or you can sit on a pillow or two．
Here is a good piece of advice： 3 ．Even if you don’t have to go to the bathroom, be sure to take breaks．Kids shouldn’t sit at a computer for more than 30 minutes without a break．
When it’s time for a break, start with the eyes． 4 ．This can give your eyes a rest from all that focusing on the computer monitor．
5 Try to move your muscles．Go for a walk or dance in front of the mirror．Doctors advise only one or two hours of screen time per day, which includes TV, the computer and computer games．Make computer time just one of the activities you do instead of the only thing you do．Your body will thank you forever!
A．Never play computer games too long．
B．Your mom or dad can help you get adjusted．
C．Then you’ll want to give your body a break, too．
D．Focus on something far away by looking out of a window．
E．Leaning your neck back or forward too long will cause pain and damage．
F．At this distance, you shouldn’t have to lean in to read what’s on the screen．
G．Don’t get so involved in the computer that you forget to go to the bathroom．
If we wish to write an equation for the chemical reaction between the elements phosphorus and oxygen, we begin with the formulae for the molecules of phosphorus and oxygen．
P4 (s) + O2 (g)---> [※s = solid , g = gas ．]
Again, we state the formulae of the molecules which react;by writing P4 and O2, we indicate or show that a molecule of phosphorus has four atoms, while a molecule of oxygen has two atoms ．
The product of this reaction is the compound phosphorus oxide:
P4 (s) + O2 (g)---> P4O10 (s)
Again wesee that a chemical unit of the new compound has two types of atoms． Each chemical unit contains or has four phosphorus atoms and ten oxygen atoms． This equation correctly gives the formulae of the reactants and the products, but, as it is written, mass is not conserved or kept． Only two atoms of oxygen enter the reaction, but ten atoms of oxygen appear in the product． This equation cannot be correct． Ten atoms of oxygen must have come from five molecules of oxygen． So we must make the following correction:
P4 (s) + 5O2 (g)---> P4O10 (s)
Now the mass of oxygen is conserved;all the oxygen atoms in the product are present in the reactants．
Now the equation is correct． Mass is conserved, and both the reactants and the products are shown by correct formulae． This process or step by which we explain all the atoms in a reaction, and so show that mass is conserved or kept throughout the reaction, is called balancing a chemical equation． A chemical equation is not correctly written until it shows that the reactants and products obey or keep to the Law of Conservation of Mass． This law of chemistry states or says that: In an ordinary chemical reaction, atoms are neither created (= newly made) nor destroyed．
In many cases or very often, both the reactants and the products of chemical reactions are compounds． But, as always, the reaction results in a rearrangement or replacing of the atoms in the reactants to form new substances or things． For example, copper (II) oxide will react with hydrochloric acid to produce a salt, copper(II) chloride, and water．
CuO(s) + HCl (2q)---Cucl2(aq) + H2O (1)
[※aq = aqua/‘æ kw¶ / =liquid solution溶液;l = liquid ．]
Since we know the reactants and the products, we begin our equation by writing correct formulae for these compounds． Then we check or examine to see whether the Law of Conservation of Mass has been observed． We can see immediately that it has not, for two atoms of chlorine appear in the products while only one atom of chlorine is shown in the reactants． So we balance the numbers of chlorine atoms and check again．
CuO(s) + 2HCl (2q)---CuCl2(aq) + H2O (l)
Now the equation is correct． It tells us that each compound has two different types of atoms． During the reaction, these atoms have “changed patterns”, so to speak, and new arrangements have been formed to produce different compounds．
We have seen that elements may react with one another to form compounds, and since compounds may also react with one another to form new substances, the number and variety of chemical reactions which may occur are almost limitless． Chemical equations are a type of chemical shorthand which we use to show these reactions, but they do not tell us what will happen when elements or compounds react． We can write a correct equation only if we know both the reactants and the products． Suppose you knew that the element zinc reacts with hydrochloric acid to produce a salt, zinc chloride, and the element hydrogen． You would begin the chemical equation by writing correct formulae to show the chemical units of the reactants and the products:
Zn(s) + HC1(aq) ® ZnCl2 (aq) +H2(g)
Correct formulae for the chemical units of both elements and compounds are necessary． (All the common gases have two atoms per molecule, and you are fairly safe in supposing that most other elements have only one atom per molecule． However, you have seen a few exceptions to this rule earlier in the chemistry book you learned at school．) If you are satisfied that your formulae are correct, balance the equation to show that the Law of Conservation of Mass is observed during the reaction． In our example you can see that the two atoms of hydrogen and the two atoms of chlorine in the chemical units of the products must have come from two chemical units of the reactant, hydrochloric acid．
We show this fact as follows:
Zn(s) + 2HC1(aq) ® ZnCl2 (aq) +H2(g)
1．Which of the following is a correct equation?
A．P4B． P4O10 C． P4 + O2 ---> P4O10 D． P4 + 5O2 ---> P4O10
2．Which of the following is an element?
A．P B． P4O10 C． H2O D． CuO + 2HCl ---> Cucl2 + H2O
3．P4 shows that it ．
A．has four atoms B． is a new compound
C．is the formula of an element D． contains or has ten oxygen atoms
4．Whichof the following is a reactant in a chemical reaction?
A．P4O10 in P4 + 5O2 ---> P4O10 B． O2 in P4 + O2 --->
C．CuO in CuO + 2HCl---> CuCl2 + H2O
D．H2 in Zn + 2HC1 ---> ZnCl2 +H2
5．Which of the following is NOT correct?
A．ZnS + HCl ---> ZnCl2 +H2S B． P4 + 5O2 ---> P4O10
C．CuO + 2HCl---> CuCl2 + H2O D． Zn + 2HCl---> ZnCl2 +H2
6．Matter is made up of ．
A．substances B． reactants and products
C．elements and compounds D． equations
7．Which of the following sayings is true?
A．Most elements have only one atom each．
B．Most gases have only one atom each．
C．Almost all elements have two atoms each．
D．Almost all gases or gas elements have two atoms each．
8．What quantities are the same on both sides of a chemical equation?
A．Molecule quantities B． Atom quantities．
C．Reactant quantities and product quantities． D． Element quantities．
9．The difference between a compound and an element is that ．
A．they have different number of atoms each
B．they have different quality of atoms each
C．the element has the same kind of atoms while the compound has not
D．the element is made up of atoms while the compound is not
10．How many molecules of sodium would be required to produce six molecules of hydrogen according to the following equation?
2Na + 2H2O ---> 2NaOH + H2
A．6． B．8． C．10． D．12．
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