It remains to be seen he will solve the problem or not. A. thatB. whatC. whichD. whether

问题补充：

It remains to be seen he will solve the problem or not.

A. that

B. what

C. which

D. whether

答案：

A. that

B. what

C. which

D. whether

解析：考察名词性从句。It是形式主语，真正的主语从句是whether he will solve the problem or not。Whether在句中不充当任何成分，指起引导作用，与or not连用。结合句意可知D正确。句意：他是否会解决这个问题有待于进一步观察。