Question

Choose the answers to the question using a direct object pronoun instead of a direct object noun. There may be more than one answer.
¿Estás coleccionando sellos?

Answer 1

Sí, colecciono sellos.

Sí, los colecciono.

Sí, los estoy coleccionando.

Sí, los coleccionando.

Answer 2

Hopefully this translation will help:

Are you collecting stamps?
a. Yes, I am collecting stamps.
b. Yes, I collect.
c. I am collecting it.
d. Yes, I am collecting.

Which one would be a more reasonable and proper way to answer this question?