Since then the number of people taking driving lessons 20%.
A. has increased to
B. increases by
C. has increased by
D. have increased
网友回答
A. has increased to
B. increases by
(答案→)C. has increased by
D. have increased
解析：考察时态。本题的关键是时间状语since then，该时间状语和现在完成时连用。句意：从那时起，参加驾驶考试的人的数量已经上升了百分之20.句中的介词by表示程度；to表示结果。故C正确。