Question

Since then the number of people taking driving lessons ________ 20％．

1. A.
   has increased to
2. B.
   increases by
3. C.
   has increased by
4. D.
   have increased by

Answer 1

C
解析：
since the意为“自那以后”，要求(主句)句子用完成时态，可排除B项；
the number of意为“……的数量”，作主语时谓语应用单数，可排除D项；
increase to意为“增加到”，后接结果；
increase by意为“增加了”，后接幅度，所以C项为最佳选项。