Memory and thinking are most closely associated with which part of the central nervous system?

Cerebrum

Explanation:

Memory is a complex process and the stored memory is the past experience of the human being. They are formed by thinking and different events done by the human.  

The cerebrum of the brain involves thinking and memory. This is the largest part of the brain having different sub-parts. They are especially the hippocampus, temporal lobe, limbic system which involves different types of memory.

Cerebrum involves in hearing, speech, movement control, learning.

The limbic system is part of the cerebral cortex. It is concerned with emotion, behavior,  memory.

The long term memory is dealt with by the hippocampus. This type of memory gets active when a person wants to recall something or memorize a thing for a long time.

The temporal lobe involves listening to a sound and store some short term memory. Other lobes of cerebrum involve sensory memory like vision, taste, smell, etc.

this is true, assuming that the allele is completely recessive and incomplete dominance is not a factor.