Since then the number of people taking driving lessons 20.A. has increased toB. increases

问题补充：

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

答案：

A. has increased to

B. increases by

(答案→)C. has increased by

D. have increased by

解析：句意：自那时以来考驾驶课程人的数目已经以20%的速度增加。since then自从那时起，用于现在完成时；by表示比率作“以…为单位”解时,常与表示单位的名词或数词连用，表示增加或减少了，to增加到；the number of做主语，谓语用单数形式。increases是一般现在时的形式。故选C。

考点: 考查动词的用法。