He explained the question again to make it easier .
A. to understand
B. understanding
C. understood
D. understand
网友回答
(答案→)A. to understand
B. understanding
C. understood
D. understand
解析：考查句型：make it+adj+to do…，使得做…如何…,it是形式宾语，不定式是真正的宾语，句意：他再次解释这个问题使它变得更容易。选A。