Question

9．An egg sinks to the bottom if you drop it into a glass of ordinary drinking water but what happens if you add salt？The results arc very interesting and can teach you some fun facts about density（密度）．
     What you'll  need：
*One egg*Water*Salt*A tall drinking glass
     Instructions：
     Pour water into the glass until it is about half full．
      Mix in lots of salt （about 6 tablespoons）．
     Carefully pour in plain water until the glass-is nearly full （be careful not to mix the salt water with the plain water）．
     Gently lower the egg into the water and watch what happens．
     What's happening？
      Salt water is denser than ordinary tap water．The denser the liquid is，the easier it is for an object to float in it．When you lower the egg into the liquid it drops through the normal tap water until it reaches the salt water，at this point the water is dense enough for the egg to float．If you were careful when you added the tap water to the salt water，they will not have mixed，enabling the egg to amazingly float in the middle of the glass．
 
21．Which of the following is the CORRECT order？B
①Mix in lots of．salt．
②Gently lower the egg into the water．
③Carefully pour in plain water until the glass is nearly full．
④Pour water into the glass until it is about half full．
A．④②①③B．④①③②C．①④③②D．③④①②
22．What will happen if you drop an egg into a glass of water with about 6 tablespoons of salt？A
A．It will float in the water．
C．Nothing will happen．
B．It will sink to the bottom．
D．The result is not known．
23．Why can the egg float in the water according to the passage？C
A．Because ordinary tap water is denser than salt water．
B．Because ordinary tap water is as dense as salt water．
C．Because'the denser the liquid is，the easier it is for an object to float in it．
D．Because the more the liquid there is，the easier it is for an object to float in it．

Answer 1

分析 短文主要介绍了一个实验，把蛋放在盐水里面，最后蛋漂浮起来的过程．

解答 21．B．细节理解题．根据文章中的"Instructions"部分可知，先倒一半的水，再加盐，再慢慢加入淡水直到满了，最后蛋就慢慢往下了，故答案为B．
22．A．细节理解题．根据文章最后一段的"…at this point the water is dense enough for the egg to float．"可知加入盐的水密度比较大，可以导致蛋漂浮起来，故答案为A．
23．C．细节理解题．根据文章最后一段"…the denser the liquid is，the easier it is for an object to float in it．"可知液体的密度比较大，物体就更容易漂浮起来，故答案为C．

点评 考查学生的细节理解和推理判断能力．做细节理解题时一定要找到文章中的原句，和题干进行比较，再做出正确选择．在做推理判断题时不要以个人的主观想象代替文章的事实，要根据文章事实进行合乎逻辑的推理判断．