After the communists gained control of China in 1949,

a. the United States repudiated the leadership of Jiang Jieshi.
b. staunch anti-communists accused President Truman of losing China to the communists.
c. most Americans recognized that their triumph resulted from a long internal conflict within that country.
d. Secretary of State Dean Acheson claimed that the United States could have prevented the communist takeover.

After the communists gained control of China in 1949,

c.most Americans recognized that their triumph resulted from a long internal conflict within that country.

Explanation:

Rise of communism in China was not something that the US could have prevented in any capacity due to the long drawn out conflict in the nation that had resulted in the communist take over by its own means

As much as the US would have wanted it to be otherwise this was to be the case without any doubts in the matter.

So, eventually the government had had to accept that fate and had to work with it as they could not boycott this china by any means.

d is the answer. leo should include the source.