Question

what new military practice was introduced during world war i?
trench warfare
foot soldiers
barbed wire
bayonets

Explanation:

Trench warfare became a prominent new military practice during World War I. Foot soldiers, barbed wire, and bayonets were used in earlier conflicts, while trench warfare was a defining and newly prominent (in its extensive use) practice in WWI, with armies digging elaborate trench systems for defense and combat.

Answer:

A. trench warfare