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。请回答下列有关问题：（1）该同学并没有注射过乙肝疫苗，就此检验结果请你分析可能的原因是 。
（2）用图解表示乙肝病毒（含有DNA）感染人体过程中的遗传信息的流动方向： 。
（3）由乙肝病毒外壳蛋白制成的乙肝疫苗，注入机体之后，将作为__________物质，使__________被激活而增殖分化形成浆细胞和__________。
（4）该同学在踢足球时不小心被铁钉扎破了脚，及时注射了破伤风抗毒素进行治疗，已知破伤风杆菌可阻止神经末梢释放甘氨酸，因而能引起肌肉痉挛和惊厥
。据此分析甘氨酸相当于一种________，它能使下一个神经元的 信号向 信号转换过程受阻。
查看习题详情和答案>>
用am，is或are填空，然后总结其用法。
(1)That's my father and this ________ my mother.
(2)This is my cousin and that ________ my sister.
(3)－________she your sister?
－Yes, she ________.
(4)－And ________ he your brother?
－No. He's my friend.
(5)－________ Guo Peng your brother?
－Yes, he ________.
(6)I ________ his friend. I'm not his brother.
(7)－________ you Jack's brother?
－No, I'm not. I ________ his cousin.
(8)These ________ my grandparents.
(9)－________ this your aunt?
－Yes, it ________.
(10)These ________ my parents, those ________ my grandfather and grandmother.
(11)These are my brothers. They ________ Jeff and Jack.
(12)They aren't my sisters. They ________ my friends.
am用于第一人称单数I之后；is用于第三人称单数ge，she，it以及相当于he，she或it；are用于第二人称或所有人称的复数，表达“是”的意思。可用下面的口诀来帮助记忆：“我用am你用are，is用于他她它，复数全都要用are”。
I am…可以缩写成I'm，he is可以缩写成 he's，she is可以缩写成加she's，it is可以缩写成it's，而we are，you are，they are可分别编写成we're，you're，they're。am，is，are的否定形式是在后面加not，如：am not，is not，are not。is not通常缩写为isn't，而are not通常缩写为aren't。如：
(1)I'm Alice, I'm not Mary. She's Mary.
(2)This isn't my brother. He's my cousin.
(3)They're my brothers. They aren't my friends.
查看习题详情和答案>>Is the world too crowded? Well, that’s a hard question to answer. It’s all a matter of perspective(视角).In Montana, you might drive for a mile in any direction and not see another human being. In Macao, 60,000 people live in every square mile!
What is true is that the world’s population doesn’t stay the same. It has been increasing at a very fast rate(比例).That’s in part because in each generation(代) these are more people who then have children than in the last generation.
Five hundred years ago, the population of the world was about 460 million. In 1900,the world’s population was under 2 billion(十亿).Right now it is doubling every 40 years. That means, if this rate of growth continues, when you are a parent, there will be twice as many people on earth as there are now. Wow! Now that’s a whole lot of people! Soon the world’s population will probably reach 7 billion. Some people worry about that! But there is a lot of disagreement about just how many people on earth equals(相当于) too many people. But everyone agrees that the more people there are, the more resources(资源) the world needs to feed, house and take care of all of them, and the more need there is to think carefully about how we live and use the earth’s resources.
【小题1】From the first paragraph we can know that ________.
| A．Montana is too crowded |
| B．Macao is too crowded |
| C．the world is too crowded |
| D．the world is not too crowded |
| A．people live longer than before |
| B．there are less wars than before |
| C．medicine is developing faster than before |
| D．more couples now would like to have children than before |
| A．450 million. | B．about 2 billion. |
| C．40 billion. | D．7 billion. |
| A．find more resources |
| B．use more resources |
| C．think about our ways of living |
| D．move to other places |
| A．thinks the world already has too many people |
| B．thinks the world can feed no more than 7 billion people |
| C．is not sure when the world’s population will reach 7 billion |
| D．is not sure what the largest population that the world can feed is |
