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