Which statements about the war in Vietnam are true? Choose all answers that are correct.
a. Once South Vietnam surrendered, the rest of Southeast Asia soon fell to communist invaders.
b. U.S. forces fought a conventional war, while their communist foes conducted a guerilla campaign.
c. The Vietnamese wanted to be free of all foreign influence.
d. The Soviet Union and communist China refused to aid North Vietnam in its bid to overrun South Vietnam.