The trip was 40 miles. The speed for the first y miles was x, and the speed for the remaining trip was 1.2x. What is the average speed（）
(1)x=12 miles per hour
(2)y=20 miles
A.条件(1)充分，但条件(2)不充分．
B.条件(2)充分，但条件(1)不充分．
C. 条件(1)和(2)单独都不充分，但条件(1)和条件(2)联合起来充分．
D. 条件(1)充分，条件(2)也充分．
E.条件(1)和条件(2)单独都不充分，条件(1)和条件(2)联合起来也不充分