You can't imagine the difficulty they had [ ] the problem.It isn't [ ] easy.

问题描述:

You can't imagine the difficulty they had [ ] the problem.It isn't [ ] easy.
A.to solve; so
B.solved; so
C.solving; that
D.solved; that
为什么?

have difficulty (in) doing something,固定搭配,只能选C
that,作“那么”解
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