33. Long-term potentiation (LTP) represents a fundamental cellular mechanism underlying learning and memory. Which of the following best describes a critical requirement for the induction of early-phase LTP? (A) Sustained activation of NMDA receptors leading to Ca2+ influx, which directly promotes rapid insertion of AMPA receptors into the postsynaptic membrane. (B) Ca2+ influx through NMDA receptors following postsynaptic depolarization, which triggers the translocation of additional AMPA receptors to the postsynaptic membrane via calcium/calmodulin-dependent protein kinase II (CaMKII) signaling. (C) Increased presynaptic glutamate release caused by enhanced vesicle docking, which by itself is sufficient to maintain persistent synaptic potentiation. (D) Activation of postsynaptic glycine receptor chloride channels, which leads to the depolarization that relieves the Mg2+ block of NMDA receptors. (E) Immediate activation of cAMP response element-binding protein (CREB)-dependent gene transcription in the absence of Ca2+ influx, which primes neurons for later potentiation.