单选题 Mercury's velocity is (so much) greater than (the Earth's) that it completes more than four revolutions around the Sun in the time (that) takes the Earth to complete (one).

A、 so much
B、 the Earth''s
C、 that
D、 one

【正确答案】 C

【答案解析】that改为(that)it。(that)it takes the Earth to complete one是定语从句，修饰先行词 time，其中 it 是形式主语，to complete one是实际主语，关系代词that是takes的宾语，可以省略。