His friends ignored his advice they knew it to be helpful.A. as ifB. sinceC. even ifD. s

问题补充：

His friends ignored his advice, they knew it to be helpful.

A. as if

B. since

C. even if

D. so that

答案：

A. as if

B. since

(答案→)C. even if

D. so that

解析：考查连词辨析。A似乎；B自从，既然；C即使；D以至于；句意：他的朋友不理睬他的建议。即使他们知道这些建议很有帮助。故C正确。