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.

B cells are a type of lymphocyte that originate from the bone marrow and are involved in humoral immunity.
When they encounter a foreign substance (antigen), they differentiate into plasma cells, which secrete antibodies.
Antibodies are proteins that bind to the antigen and neutralize it.
Choice A is wrong because megakaryocytes are large cells that produce platelets, not antibodies.
Choice C is wrong because antibodies are not cells, but products of plasma cells.
Choice D is wrong because T cells are another type of lymphocyte that originate from the thymus and are involved in cell-mediated immunity, not antibody production.

This is because ventricular systole is the phase of the cardiac cycle when the ventricles contract and pump blood into the arteries.
The blood pressure in the arteries is greatest during this phase because of the forceful ejection of blood.
Choice B.
Atrial diastole is wrong because atrial diastole is the phase of the cardiac cycle when the atria relax and fill with blood from the veins.
The blood pressure in the arteries is lowest during this phase because the ventricles are also relaxed and not pumping blood.
Choice C.
Ventricular diastole is wrong because ventricular diastole is the phase of the cardiac cycle when the ventricles relax and fill with blood from the atria.
The blood pressure in the arteries is low during this phase because the ventricles are not pumping blood.
Choice D.
Atrial systole is wrong because atrial systole is the phase of the cardiac cycle when the atria contract and push blood into the ventricles.
The blood pressure in the arteries is not affected by this phase because the ventricles are still relaxed and not pumping blood.
The normal range for systolic blood pressure is less than 120 mm Hg and for diastolic blood pressure is less than 80 mm Hg.