高一的英语选择填空（求解答）
this letter was sent by_______
      A.a friend of my father’s                 B.a friend of my father
但是为什么选A,B不可以吗?
   2.the laboratory assistant recorded the ___ reactions(反应）.
A.mouses’    B.mice’
不过这里的老鼠不是泛指吗?泛指就要用mouse,怎么还是mice呢?
   3.you will find this map of great ____ in helping you to gei round London
 A.value  B.usefulness
答案为A但是这两者意思一样,怎么区分选C呢?
   4.The new law will come into ___ on the day it is passed.
 A.effect  B.use C.service D.existence
这个能给我讲讲吗?
   5.One of the advantages of living on the top floor of a high-rise is that you can get a good ____
A,sight B.view
两者都有视野的意思,为什么答案是B