Glutamate is released for tens of seconds onto neurons in a slice of brain in a dish. Drugs that block the sodium channels needed for spiking have been added to the extracellular fluid. The glutamate binds to postsynaptic glutamate receptors, opening ion channels with a reversal potential of 0mV. This depolarizes neurons towards 0mV. However, the depolarization does not reach all the way to 0mV, because:

A. The glutamate receptor channels open, but the channels close before there has been enough time for the membrane to reach 0mV.
B. The glutamate receptor channels open, but the channels inactivate before there has been enough time for the membrane to reach 0mV.
C. The glutamate receptor channels open, but the leak channels that maintain the resting membrane potential remain open and try to keep the membrane near -70mV, so the membrane potential reaches a value that is intermediate between the reversal potential of the glutamate receptor channels and the leak channels.
D. The glutamate channels are permeable to potassium, which has a reversal potential near -90mV.
E. The glutamate channels initiate a suprathreshold depolarization, initiating action potentials that drive the membrane past 0mV, towards +50mV.