Mercury’s velocity is so much greater than the Earth’s that it completes more than four

选B.
(4)名词短语、介词短语each /every time,the moment/second/minute,
in the time,by the time起连词作用.如:
I hope her health will have improved greatly by the time we come back next year.
My pain must have been apparent the moment I walked into the room,
for the first man I met asked sympathetically:“Are you feeling all right?”
Mercury’s velocity is so much greater than the Earth’s that it completes more than four
revolutions around the Sun in the time it takes the Earth to complete one.