Which of the following factors was a reason for the United States' decision not to fortify the Philippines more heavily prior to WWII? a.

The US planned to use its naval forces at Pearl Harbor to support the Philippines as backup.
b.

The US decided to protect Corregidor and the Philippines with diplomacy instead of weapons.
c.

The "Non-fortification Clause" of a treaty restricted the US from building up certain kinds of defenses.
d.

All of the above were factors in this decision.