What was the name of the theory that said if one country in a region fell to communism, others would surely follow ?

a) domino theory
b) arms race
c) brinkmanship
d) containment theory

The domino theory was a theory used from the 1950s to the 1980s that stated "if one country falls to communism, then the surrounding countries would fall to communism."

Thus, the correct answer is a) domino theory.

I hope this helped!

the three answers (for plato at least) are:

b-condemned sola fida 

d-set rules for establishing seminaries and for educating clerics in the seminaries 

f-recommended moderation in the sale of indulgences and banned the sale of false indulgences 

the answer is