Problem with extruding polygons

PhoenixCreates

I'm following a tutorial on modelling and at some point I have to extrude downwards to make the inside of a dumpster, tough as I extrude, 2 polygons remain and I can't figure out why.

MELKIY

Choose "Group" option instead of "By polygon".

PhoenixCreates

Thank you for taking your time to answer such a simple question. It worked.