Why Did Soviet-American Relations Become Strained in 1960

Multiple Choice

Why did Soviet-American relations become strained in 1960?

A) A Soviet spy plane was shot down within U.S. borders.
B) An American spy plane was shot down within Soviet borders.
C) The Soviets resumed atmospheric tests of nuclear weapons.
D) The United States discovered that Soviet missiles had been installed in Cuba.
E) The United States resumed atmospheric tests of nuclear weapons.