¿le interesa el fútbol a pedro?
sí. le interesa.
sí. te interesa.
sí. le interesan.
sí. se interesa.

First of all, the word sí tells us that this is an affirmative sentence. Although, all the other options start with this word. However, we choose this option because because of the word le and interesa. So le is the indirect object pronoun for the third person singular. On the other hand, since futbol is a singular noun, we must use interesa that comes from the verb interesar. So an Indirect Object Pronoun is a person that receives the action of a verb indirectly. Its purpose is to tell you to whom or for whom something is done. In this sentence, the action is being performed for Pedro, that is, for him. So:

Sí. Le interesa.