Question

in ww1, a new weapon fired 500 rounds a minute, changing combat. what was it? pistol machine gun tank smoke bomb

Explanation:

In World War I, machine guns were new weapons that could fire at a high rate, around 500 rounds per minute, and significantly changed combat tactics. Pistols have a much lower firing rate, tanks are armored vehicles (not primarily defined by round - firing rate in this way), and smoke bombs are for obscuring, not rapid firing. So the correct answer is the machine gun.

Answer:

B. Machine gun