What initially brought the United States into the conflict in Vietnam?

Question $7$ options:

a$)$

a desire to keep China from taking over the country

b$)$

a need for a place to wage a proxy war with Soviet Communism

c$)$

a promise to aid the French as they fought to preserve their colonial control

d$)$

the supporters of the $$China lobby$$ who wanted to involve the United States in Asia by any means they could