Why was the Ho Chi Minh trail important to the North Vietnamese and the NLF?

Why was the Ho Chi Minh trail important to the North Vietnamese and the NLF?

a. The trail was a pass around a U.S. naval blockade.
b. The trail connected North Vietnam to China.
c. The trail was a route to move goods to allies in South Vietnam.
d. The trail connected North Vietnam with Laos.