What was NOT a cause of many casualties during World War I?

A. mustard gas

B. trench warfare

C. atomic bombs

D. hand grenades

C. atomic bombs

Explanation:

The World War I was a war in which lot of new weapons were used, and they caused millions of deaths unfortunately. Some of the new weapons used were the mustard gas and the hand grenades, both used in close combat, and being able to either kill the enemy or immobilize it, thus giving advantage to the ones using them. The atomic bombs though were not part of the new weapons used int he World War I. The atomic bombs were first used in the World War II, but they were still not invented and developed for the World War I, so they were not used in it.