Final answer:
Choline is the molecule that must be actively taken up by cholinergic neurons to synthesize the neurotransmitter acetylcholine (ACh). Option D.
Step-by-step explanation:
The correct answer to the question is D) Choline. Choline must be actively taken up by cholinergic neurons in order to synthesize the neurotransmitter acetylcholine (ACh). During neurotransmission, ACh is released from the presynaptic neuron into the synaptic cleft and binds to ACh receptors on the postsynaptic membrane.
The liberated choline from the breakdown of ACh is then taken up again by the presynaptic neuron. Acetylcholine is synthesized by combining the reclaimed choline with acetyl-CoA, a reaction facilitated by the enzyme choline acetyltransferase.
Option D.