Explanation

 p24:

This protein is part of the Gag protein complex, which is responsible for forming the viral core.

The matrix is the layer surrounding the viral core, and p24 is the primary structural component of this matrix. 

gp120 and gp41:

These are glycoproteins on the surface of the HIV envelope.

They are involved in viral attachment to and entry into host cells, but not the formation of the matrix.