One major ______ of space travel is the radiation that exists beyond Earths atmosphere.A.m

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One major ______ of space travel is the radiation that exists beyond Earths atmosphere.

A.mystery

B.reward

C.goal

D.hazard

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_________。