Answer :
The correct answer is option A. "the Soviet Union built them too". The nuclear arms race took place during Cold War, and was a competition for supremacy in nuclear warfare between the United States and the Soviet Union. Under this competition if the United States built hydrogen bombs, the Soviet Union would built them too in order to stay in line with his competitor.
It should be noted that the Arms race simply means that if United States build hydrogen bombs, A. the Soviet Union built them too.
What is arms race all about?
Arms race serves a pattern of competitive acquisition of military capability between two or more countries. It refer to any military build up or spending increases by a group of countries.
The reason why the Soviet Union vowed to build hydrogen bomb if United States build bombs was that they were seeking for supremacy in terms of nuclear weapons manufacturing.
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