Question

Since three months ago, the number of students making notes while listening in class ________ 90％．

1. A.
   has increased by
2. B.
   was increased to
3. C.
   have increased for
4. D.
   had increased by

Answer 1

A
since three months ago是现在完成时的时间状语，所以句子的时态要用现在完成时。increase by 意思是“增长了多少”，而increase to为“增长到(一个具体的数字)”。the number of students意思是“学生的数目”，谓语动词应该用单数形式。