Holes in the ceiling

Hi,

I am new to the forum and as my Denali is new to me. I have a question about the two holes that are in the ceiling in the rear passenger compartment. Are they supposed to be there? I bought mine used and the dealer said they were ventilation holes. I really don't believe him so I am wondering if there is some kind of plug that is supposed to be there.

TIA

Eric

They are ventilation holes, the grills are missing.
You can get the parts from GM parts.
They twist in,

Thanks for the reply