Why Are Biological Treatments for Major Neurocognitive Disorder Usually Ineffective

Why are biological treatments for major neurocognitive disorder usually ineffective?

A) The damage is too extensive.
B) Medications that improve cognitive functioning have unpleasant physical side effects, so patients refuse to take them.
C) Medications to treat major neurocognitive disorder only work on a small segment of sufferers with a very specific type of tissue damage.
D) Treatments are very expensive, and thousands of treatments are needed for any effect to be seen.