单选题 6. A rocket does not depend on the atmosphere for its propulsion, but ______ in the absence of an atmosphere because of lessened air resistance.

A、 would actually perform better
B、 perform better
C、 performed better
D、 have had performed better

【正确答案】 A

【答案解析】 火箭推力的产生并不依赖于大气，但是，假如没有大气的话，由于空气阻力减小，火箭实际上会运行得更好。
虚拟语气题。虚拟语气以非真实条件句为代表。本题属于含蓄条件句，同样引出非真实情况，即in the absence of an atmosphere表示虚拟的条件，与客观事实相反，而选项相当于主句的谓语，应使用would do形式，故本题答案为A。