An old man with steel-rimmed spectacles and very dusty clothes sat by the side of the road. There was a pontoon bridge across the river and carts, trucks, and men, women and children were crossing it. The mule-drawn carts staggered up the steep bank from the bridge with soldiers helping to push against the spokes of the wheels. The trucks wound up and away heading out of it all. The peasants plodded along in the ankle-deep dust. But the old man sat there without moving.
The soldiers were ''helping to push against the spokes of the wheels'' because :

Options

A. they wanted to stop the carts
B. the spokes of the wheels were broken
C. the mules refused to draw the carts
D. there was a steep elevation