In cells where the equilibrium potential for Cl- equals the resting potential, opening Cl- channels ...

In cells where the equilibrium potential for Cl- equals the resting potential, opening Cl- channels in the subsynaptic membrane
 a. has no effect on the probability of the postsynaptic cell reaching threshold since there's no movement of Cl-.
  b. increases the probability of the postsynaptic cell reaching threshold since the entry of Na+ into the cell (through another route) will make the cell less negative and allow Cl- to leave the cell, offsetting the effect of Na+.
  c. decreases the probability of the postsynaptic cell reaching threshold since the entry of Na+ into the cell (through another route) will make the cell less negative and Cl- will enter the cell, offsetting the depolarizing effect of Na+.
  d. none of these.