do, to do, or doing

The first thing I like to do in my free time is … to music.
Which one of the following is the right answer to fill in the gap?
A. To listen
B. Listen
C. Listening
Could you tell me the generalization?

Hi Genzo,
I’d pick up:

The first thing I like to do in my free time is listening to music.

Hi,

The answer for me would simply be: listen. The reason for this is that the verb is dependent on ‘like’. The sentence reads: The first thing I like to do … is I like (to) listen to music.

Alan