Answer:
To sing.
Step-by-step explanation:
A mi amigo le gusta cantar is Spanish for: My friend likes to sing. Therefore, I am assuming the underlined word would have been cantar, which means to sing. As sing is one of your options, one would assume that the proper answer would be sing.
Hope this helps, and I apologize if this is inaccurate as there was no word that was underlined in this question.
Have a great day! :D