"It doesn't happen very often, but it does happen in the capital city of the United States." It refers to ______.

A．he didn't have much money to give them
B．he laughed at them
C．they belonged to a different political party
D．he was not afraid of them

A．China did not belong to W. H. O.
B．doctors in Asia did not recognize the disease
C．reporting procedures were not good enough
D．the people who caught it were travellers