The correct answer is A. ions.
An electrolyte is a substance that, in solution, separates into ions and conducts electricity. The movement of ions through an electrolyte is what causes current to flow.
Holes are not particles, but rather regions of an electron-deficient semiconductor crystal lattice. They can be thought of as positive charges that move through the crystal when an electron is removed from its position. However, holes do not actually exist as particles; they are simply a way of describing the movement of electrons.
Electrons are negatively charged particles that are found in atoms. They are responsible for the flow of electricity in conductors.
Therefore, the only option that correctly describes the movement of current through an electrolyte is A. ions.