Alzheimer's disease is a chronic neurodegenerative (progressive loss of structure or function of neurons, including death of neurons) disease that usually starts slowly and worsens over time.
Acetylcholine (ACh), a neurotransmitter essential for processing memory and learning, is decreased in both concentration and function in patients with Alzheimer's disease. This eventually leads to memory loss (Dementia)
So, the correct answer is 'Both A and B'.