The problem he referred to difficult, but is isn’t at all.
A. must be
B. seeming
C. seems
D. seem
网友回答
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。