Symptoms are likely to begin appearing and the person is vulnerable to opportunistic infections and certain tumors when the number of t4 cells drops below which level?
a. 200/cubic millimeter
b. 400/cubic millimeter
c. 800/cubic millimeter
d. 600/cubic millimeter

200/cubic millimeter.

Explanation:

An opportunistic infection may be defined as the infection that normally do not affect but become pathogenic in the favorable environment. The individual with the weakened immune system gets the opportunistic infection more than the normal individual.

The blood tests are performed to check whether the individual has the opportunistic infection or not. The drop of the level of the T4 cells below the 200/cubic millimeter clearly indicates the case of the opportunistic infection in the individual.

Thus, the correct answer is option (A).