题目内容:
Itisdifficulttosendpeopletootherplanetsbecauseof
A.lackofcapacityofspaceexplorationvehicles. B.thefinancialexpenditureinvolvedinspacetravel.
C.controversialnatureofspacetravel.
D.theuncertainfutureofspaceexploration.
参考答案:
答案解析: