The average speed of a train running at a speed of 30 km/h during the first 100 km, at the speed of 40 km/h during the second 100 km and at the speed of 50 km/h during the last 100 km is nearly ________.

A

40.2 km/h

B

38.3 km/h

C

39.2 km/h

D

37.5 km/h