There are many proteins in the cell that can be grouped depending on when you find them: they can be internal proteins, transmembranal proteins, etc.
In this question, internal proteins refer to the ones that are in the interior of the cell, not attached to the membrane.
Let's take a look at the functions listed:
Cell adhesion (a) involves the interaction of the cell with other cells or the extracellular matrix, so internal proteins are unlikely to be involved.
Cell to cell recognition (d) is also mostly about the interaction of the cell with its surroundings, so it wouldn't be largely affected.
Transport in/out of the cell (b) requires the involvement of transmembrane proteins, so even if it connects with the interior of the cell, it wouldn't be affected.
Cytoskeleton attachment (c) occurs in the interior of the cell, as is where the cytoskeleton is found. The cytoskeleton has several structural functions and is attached to the membrane but also to the different organelles in the interior of the cell, so this would be affected if the internal proteins were removed from the cell.