问题补充：
Students should do everything they can their study.
A. improve
B. to improve
C. improving
D. improved
答案：
A. improve
(答案→)B. to improve
C. improving
D. improved
解析：考查非谓语动词.句意:学生们应该做任何他们能做的事情来提高他们的学习. they can为后置定语,动词不定式做目的状语,表示具体的将要进行的动作,结合语境可知选B.
