Read the following SAT test question and then click on a button to select your answer.

A woman drove to work at an average speed of 40 miles per hour and returned along the same route at 30 miles per hour. If her total traveling time was 1 hour, what was the total number of miles in the round trip?

(A) 30
(B) 30(1/7)
(C) 34(2/7)
(D) 35
(E) 40

来源:可可英语 http://www.kekenet.com/sat/201411/343820.shtml