A marked decrease in brain processing and memory in some older adults is MOST likely caused by: A. inadequate control processes. B. more neural fluid that slows cerebral blood flow. C. increased production of neurotransmitters. D. the use of both hemispheres of the brain.

Option-B

Explanation:

The brain is an organ composed of neurons which controls all the voluntary and involuntary of animals.  In humans, the brain is located in the skull where the brain is suspended in a fluid called cerebrospinal fluid.

As humans ages and becomes old aged, the neurons in the brain losing their ability to perform their function, if they are lost they cannot be regenerated.

The lesions appear on the white matter of the brain and the brain shrink. Due to these known and other unknown features, the process controlled by these neurons become inadequate and shows slower brain processing and weak memory.

Thus, Option-B is the correct answer.