What event brought the communists to the forefront of vietnamese politics and government?

The Party formed an association for the independence of Vietnam named Viet Minh Front which was dominated by the Communist Party.

The association was ejecting and killed during 1945, in 1946 the political enemy was jailed and exiled after a failure to raise an overthrow against the government. In the same year, the communalists eventually suppressed all non-communist parties.

The association wrote and composed a letter to United States president asking for a support from the U.S in gaining independence for Vietnam but sadly it was ignored. This nonfulfillment seems further adopt comprehensive positions that made the association believes that it is the right choice for the country to acquire independence and liberty. 

the answer to your question is a. the salt plains

in 1811, he led an expedition, known as the george c. sibley expedition, to improve relations with the pawnee and kansa tribes, and also to locate the rumored jefferson's salt mountain