Since then the number of people taking driving lessons 20％.
A. has increased to
B. increases by
C. has increased by
D. have increased by
网友回答
A. has increased to
B. increases by
(答案→)C. has increased by
D. have increased by
解析：这题考查时态和介词的用法：时间状语是：since then，句子用现在完成时，increase by“增加了”，increase to增加到，句意是：自从那时起，上驾校的人的数量就增加了20%。选C。