Answer:
a. A non-competitive inhibitor of acetylcholinesterase.
Step-by-step explanation:
The enzyme acetylcholinesterase breaks the molecule of acetylcholine, so to maintain the levels of this substance higher in the brain, the medication must act directly in the enzyme.
An enzyme can be inactivated by higher temperatures, changes in pH and changes in the osmotic pressure, but these things would probably damage other enzymes in the brain. So, the medication must be an inhibitor of acetylcholinesterase. It would be selective and would stop the actions of the enzyme.
But, this inhibitor can't be competitive because if this happens, it would break the acetylcholine, and wouldn't solve the problem.