As shown in the figure, it is a schematic diagram of the 400m runway of the track and field stadium, which can be regarded as consisting of two semi-circular arcs and two straight lines, with the length of1000 mm, and one athlete participates in the competition alone. A, the displacement of 200m race is less than 200m, and the displacement of 100m race is equal to 100m. So, A is wrong.

B, because the displacement of 200m race is less than 200m, the time is 20.0s, and the average speed is less than 10m/s, so B is wrong and C is right.

D, the average speed is equal to the ratio of distance to time, the average speed of 100m running is v1=1001m/s, and the average speed of 200m running is V2 = 20020m/s =/kloc-0.

So choose C.