Final answer:
The incorrect statement about acetylcholine is that it is suitable for oral administration only, as acetylcholine is quickly hydrolyzed in the body, making such administration impractical.
Step-by-step explanation:
The incorrect thesis about acetylcholine is: b) it is suitable for oral administration only. Acetylcholine is a neurotransmitter that acts at the neurological junctions and in various parts of the autonomic nervous system. In fact, statement a) is correct as acetylcholine acts as a neurotransmitter at a preganglionic level in both parasympathetic and sympathetic systems. Statement c) is accurate since acetylcholine stimulates both nicotinic and muscarinic receptors. Lastly, statement d) is also true as acetylcholine does possess a very short half-life; it quickly degrades in the synaptic cleft. Acetylcholine's oral administration is not practical due to its rapid hydrolysis by the enzyme acetylcholinesterase in the body.