_out many approaches,they failed to solve the problem A.Tried B.Trying C.To try D.Having tried
问题描述：
_out many approaches,they failed to solve the problem A.Tried B.Trying C.To try D.Having tried
答
D
现在分词短语作状语,由于try out...和逻辑主语they 为主动关系,故用现在分词.再由于try out .是先于谓语动词failed 发生的,所以用现在分词的完成式Having tried out.