The effect of stress on the immune system a. is unknown. b. may involve enhancement or impairment the immune system. c. has been demonstrated to be non-existent in studies. d. most often involves enhancement of the immune system.

The correct answer is B. May involve enhancement or impairment of the immune system.

Explanation:

Stress for a shorter time period can be lead to an enhancement of the immune system as it increases the essential alert system of the body and regulates it.

However, stress for a longer period reduces the ability of the immune system to fight with antigens that can lead to infection and suppressing of the lymphocytes.

Thus, the correct answer is B.

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