The correct option is C Reduction in the number of Helper-T cells
AIDS or Aquired ImmunoDeficiency Syndrome is a fatal sexually transmitted disease that is caused by the Human Immunodeficiency Virus (HIV).
HIV attacks and destroys the helper T lymphocytes or helper T cells in the body.
The helper T cells in the body are responsible for the stimulation of B lymphocytes to produce antibodies against antigens/virus and triggering the cytotoxic T cells to kill any foreign cell that enters the body.
Thus their destruction causes a severe deficiency in the immune system, making the person vulnerable to opportunistic infections which can only attack when the immunity is compromised