Television programs are careful to add the right sound bite, a small clip of sound and image. with the information given in the sentence, a sound bite is
a. a television program
b. careful
c. a small clip of sound and image

The statement itself says that the right sound bite is a small clip
of sound and image.  When you look through the list of possible
choices for your answer, you don't find that exact word phrase until
you get to choice-c. That one says"a small clip of sound and image". 
When you see this, you realize that it's exactly the same word phrase
that you read in the question, so you know that choice-c is the choice
to select if you want the correct answer to the question.