The train was by a heavy snowfall.
A. held back B. held out C. held off D. held up

Held Up

Explanation:  If we take each option and place it in the blank of the sentence, we can see which one makes the most sense.

A. The train was held back by a heavy snowfall.

B. The train was held out by a heavy snowfall.

C. The train was held off by a heavy snowfall.

D. The train was held up by a heavy snowfall.

im going to need some more info to answer this qeustion for you