单选题 The most important consideration for manned space flight is that the rocket be ______.

A、 inexpensive to construct
B、 capable of lifting heavy spacecraft into orbit
C、 easily controlled
D、 inexpensive to operate

【正确答案】 C

【答案解析】文中提到manned space flight needs the fine adjustments only be provided by liquid fuels，而前文讲了液体燃料火箭rocket engine can be stopped completely：it can be re-ignited when desired，可以判断manned space flight对火箭最重要的要求是易于操控，选项C正确。