Which answer shows all the like terms in this list

4x, 1/2x, 2y, 4, x, 3x

You haven't shared the answer choices.

Let's rewrite that first x term: { 4x, (1/2) x, 2y, 4, x, 3x), also leaving more space between the answer choices.

I see four x-terms in { 4x, (1/2) x, 2y, 4, x, 3x }. The like terms are {4x, (1/2) x, x, 3x }. There are no other groups of like terms.