Why Was Truman Accused of "Losing" China

Why was Truman accused of "losing" China?

A) China sided with North Korea instead of the U.S.
B) China refused to join the United Nations.
C) China entered a secret pact with the Soviet Union.
D) China declared the Open Door Policy null and void, closing the door to vast exports of U.S. products.
E) China, an ally during World War II, had fallen to communism despite U.S. efforts to prevent it.