The Soviet Move Against the "Prague Spring" in 1968 Demonstrated

The Soviet move against the "Prague Spring" in 1968 demonstrated what became known as the "Brezhnev Doctrine", namely:

A) That the Soviet Union would forcibly restrain any member country attempting to abandon socialism and the Soviet alliance.
B) That experimentation with free market principles would serve as a model for other Warsaw Pact states.
C) That attempts to centralize power in the Warsaw Pact states and impose new censorship restrictions would not be tolerated.
D) That Maoist doctrine was not compatible with Soviet Communism.