Why Was Truman Accused of "Losing" China

Why was Truman accused of "losing" China?

A) China had sided with North Korea instead of with the US. and South Korea.
B) China refused to join the United Nations.
C) China entered a secret pact with the Soviet Union in 1948.
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.