问题补充：
Many problems concerning the improvement of our school remain .
A. solving
B. solved
C. to solve
D. to be solved
答案：
A. solving
B. solved
C. to solve
(答案→)D. to be solved
解析：考察非谓语动词。句意：有关改善我们学校的许多问题仍旧有待解决。不定式做表语表示具体的将要进行的动作，本句中句子主语是解决的对象，故用被动语态的不定式，选D。
