The problem he referred to difficult but is isn’t at all.A. must beB. seemingC. seemsD.

问题补充：

The problem he referred to difficult, but is isn’t at all.

A. must be

B. seeming

C. seems

D. seem

答案：

A. must be

B. seeming

(答案→)C. seems

D. seem

解析：考查seem的用法。句意“他指的那个问题似乎很难，但是一点也不（难）。”主语是The problem，he referred to是定语从句，主语是单数，故谓语也用单数。Seem是系动词，后加形容词，构成系表结构。故选C。