I'll give brainleyist to who ever helps me first please help me out

Which of the following were reasons for the high death toll caused by World War I?
Select the two correct answers.

A. Trench warfare made battles long and nearly impossible to win.
B. Influenza spread across Europe and killed civilians and soldiers.
C. Soldiers began using poisonous gas during battles.
D. Troops did not have enough food supplies and often starved.​