The red blood cells of type AB blood have on their surfaces:

The correct answer is choice A. True.

Blood flow through a capillary is controlled by a precapillary sphincter, which opens or closes due to the requirements of the cells supplied by the capillary.

This allows blood to bypass the capillaries when they are not needed and to increase blood flow when they are needed.

Choice B. False is wrong because it contradicts the true statement in choice A. A precapillary sphincter is a ring of smooth muscle that surrounds the entrance of a capillary and regulates blood flow into it.

It is influenced by local factors such as oxygen, carbon dioxide, pH, and temperature.

Macrophages are the main cells that clear out the cell debris by phagocytosis, a process that involves recognition, engulfment, and degradation of the disposable particles.

Macrophages are professional phagocytes that can be found in various tissues and organs, where they perform efferocytosis, the removal of dead and dying cells.

Choice A is wrong because lymphocytes are not phagocytes, but rather immune cells that mediate adaptive immunity by producing antibodies or killing infected cells.

Choice B is wrong because cytokines are not cells, but rather soluble molecules that regulate inflammation and immunity by acting as signals between cells.

Choice C is wrong because mast cells are not primarily involved in clearing cell debris, but rather in allergic reactions and innate immunity by releasing histamine and other mediators.