What was the most likely reason that many Americans feared the Soviet Union during the Second Red Scare in the 1950s?

A.
They believed that communist subversives were trying to overthrow the US government.
B.
They believed that the US labor unions were increasingly under the influence of communists.
C.
They believed that the US educational system was teaching their children to be communists.
D.
They believed that communist spies were in commanding positions in the US armed forces.