Help with Commands

Question

I'm learning Affirmative Familiar Singular Imperatives. Otherwise known to me as "the tú command" because the formal name is overwhelming!

My book shows these examples for Direct Objects Pronouns:

¡Ciérrala!
¡Cómela!
¡Ábrela!
¡Hazlo!
¡Ponlo aquí!

My question is - how do I know whether it's a "la" or "lo"? Logically, it would depend on the object but they neglected to mention that in the book so I want to make sure. If someone can explain this to me in a very simple way I'd appreciate it so much. ¡Muchas Gracias!