Question

the main purpose of the selective service act of 1917 was to
increase the size of the armed forces by using the draft.
restrict membership in the armed forces to those with prior combat experience.
allow all branches of the armed forces to be sent to europe.
equip the armed forces with the necessary weaponry for battle.

Explanation:

The Selective Service Act of 1917 established conscription (the draft) in the U.S. during World War I. Its core goal was to raise a large military force quickly, as voluntary enlistment was insufficient for wartime needs.

Answer:

increase the size of the armed forces by using the draft.