答案：C

解析：

Let t represent the time it took the woman to drive to work. Since her total traveling time was 1 hour, the time it took her to return home is 1-t. The distance in miles can be found using the formula distance = (rate)(time). The distance traveled to work is 40t, and the return distance is 30(1-t). Since the distance to work is the same as the return distance, 40t = 30(1-t). Solving for t yields t = (3/7). So the distance one way is 40(3/7) = (120/7) = 17 and (1/7) miles. The total number of miles in the round trip is 2(17 and (1/7)), or 34 and (2/7) miles.