单选题 According to the passage, the most difficult task of fining a rocket is ______.

A、 to get the rocket into the space
B、 to calculate the rocket's velocity of escape
C、 to guide the rocket after it leaves the Earth's surface
D、 to identify the gravitational fields of the Earth and the moon

【正确答案】 C

【答案解析】[解析] 本题的依据句是“The problem of rocket travel is not so much concerned with getting the rocket into space as it is with guiding the rocket after it leaves the Earth's surface．”从中可知C项为正确答案。