Answer:
Let the number of kinds of amplifiers be "a".
Antonio has 4 choices for the stereo and 3 choices for the speakers. Therefore, the total number of different choices he can make is:
4 (choices of stereos) x 3 (choices of speakers) x a (choices of amplifiers) = 12a
We are given that he has 36 different choices, so:
12a = 36
Dividing both sides by 12, we get:
a = 3
Therefore, there must be 3 kinds of amplifiers.
The answer is (B) 3.