Read the passage carefully and answer Q.
An 8000 kg engine pulls a train of 5 wagons, each of 2000 kg, along a horizontal track. If the engine exerts a force of 40000 N and the track offers a frictional force of 5000 N. The force of wagon 1 on wagon 2 is
(A) 28000 N
(B) 18000 N
(C) 10000 N
(D) 20000 N