问题补充：
单选题Havingmasteredthetechnologiesofmannedspacecraft,Chinabecamethethirdcountryintheworld______mannedspaceflightindependently.A.developB.to developC.developingD.developed
答案：
B解析这题考察不定式做定语的用法,当名词被序数词修饰时,应当用不定式做定语,就像这道题:the third country in the world后面接不定式做定语.句意是:掌握了载人飞船的技术后,中国成为世界上第三个独立进行载人飞行的国家.选B.
