Hard______they tried they failed to climb to the mountain topA.ifB.when.C.asD.since

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Hard______they tried, they failed to climb to the mountain top

A.if

B.when.

C.as

D.since

请帮忙给出正确答案和分析,谢谢!

热搜:关于氨基酸代谢错误的论述是_________。