题目内容:
NASAthinksspacetravellersmust__________todoprivatespacetravel.
A.observesafetymeasurescarefully B.haveanewdesiretousespacevehiclesforciviliantravel
C.negotiatewithRussiaorNASA
D.beasrichasDennisTitoandMarkShuttleworth
参考答案:
答案解析: