Under What Circumstances Did the Cold War Become a "Hot

Under what circumstances did the Cold War become a "hot" war?

A) It became a hot war when the United States and the Soviet Union became involved in armed conflict.
B) It became a hot war when the Soviet Union enforced its will on its Eastern European satellite states.
C) It became a hot war when the United States and the Soviet Union armed their Third World allies and encouraged proxy wars.
D) It became a hot war when the United States and the Soviet Union established foreign military bases in Third World countries.