Cardiac output is calculated by multiplying the stroke volume by the systolic blood pressure.

Paracrine secretions are chemical signals that affect only nearby cells.

They are released by the sending cell and diffuse through the extracellular space to the target cell, which has a specific receptor for the signal.
Paracrine signaling is a form of local signaling that occurs in multicellular organisms.
Choice A is wrong because autocrine secretions are chemical signals that act on the same cell that produced them.
Autocrine signaling is also a form of local signaling, but it involves cell signaling itself.
Choice B is wrong because endocrine secretions are chemical signals that are secreted into the blood and act at long distances.
Endocrine signaling is a form of long-range signaling that involves ductless glands that secrete hormones.
Choice C is wrong because exocrine secretions are non-hormonal substances that are secreted into ducts to the external environment.
Exocrine signaling is not a form of cell-cell communication, but rather a way of releasing substances such as sweat, saliva, or digestive enzymes.

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.