When you have a row of dominoes set up, you knock over the first one, and what happens to the last one is the certainty that the last one will go over very quickly.
That was the U.S. fear about Communism. If one country became communist, the neighboring country would fall to communism just as the dominoes would fall.
The proper answer is D. All the above
Sarcasm, humor, denial, and possibly even deflecting.
