英语智力题I have two minutes in which to catch a train , and two

英语智力题
I have two minutes in which to catch a train , and two miles to go . If I go the first mile at the rate (速率) of 30 miles per(每) hour ,at what rate must I go the second mile in order to catch the train ?
A.30pm.h b.45mp.h c.60mp.h d.90mp.h
D的答案是对的吗，有没有不一样的了？？？