The machine gun did all of the following, except
a. enabled soldiers to kill from a distance.
c. increased war casualties.
b. made the foot soldier unnecessary.
d. made total war necessary.

A machine gun is still carried by soldiers, more specifically by the infantry, that is soldiers who fight on foot: this means that foot soldiers are still necessary for the usage of machine guns, so the correct answer is b!

Also, it did enable soldiers to kill from distance and increased war casualties - because it was a more efficient weapon.