Question

The US was called the Arsenal of Democracy because
It was the country where all weapons were kept.
It provided supplies for the Axis war effort, not just the US effort.
It provided supplies for the Allied war effort, not just the US effort.
It was the country where all aircraft were housed.

Answer 1

It provided supplies for the Allied war effort, not just the US effort.

(FDR called the US the "Arsenal of Democracy" to describe its role in mass-producing weapons, planes, ships and other materiel to supply Britain and other Allies — especially under Lend-Lease — before and during U.S. entry into WWII.)