A hormone is a secreted molecule that is carried in the bloodstream to where it acts on target cells that bear specific receptors for that hormone.

T lymphocytes, also known as T cells, are a type of white blood cell that is an essential part of the immune system.
T cells are one of two primary types of lymphocytes — B cells being the second type — that determine the specificity of immune response to antigens (foreign substances) in the body.
T cells can be distinguished from other lymphocytes by the presence of a T-cell receptor (TCR) on their cell surface.
T cells originate in the bone marrow and mature in the thymus.
After migration to the thymus, the precursor cells mature into several distinct types of T cells.
One of these types is the CD8+ T cell, also known as cytotoxic T cell, which is responsible for cell-mediated immunity.
Cell-mediated immunity is the type of immunity that involves the direct killing of infected cells and cancer cells by cytotoxic T cells.
Choice A is wrong because humoral immunity is the type of immunity that involves the production of antibodies by B cells and plasma cells.
Antibodies are proteins that bind to specific antigens and mark them for destruction by other immune cells.
Choice C is wrong because programming macrophages is not a function of T lymphocytes.
Macrophages are a type of phagocytic cell that can engulf and digest pathogens and cellular debris.
Macrophages can be activated by cytokines, which are chemical messengers secreted by helper T cells and other immune cells.
Choice D is wrong because producing antibodies is not a function of T lymphocytes.
As mentioned above, antibodies are produced by B cells and plasma cells, which are another type of lymphocyte.

The endocardium is the thin inner lining of the heart chambers and also forms the surface of the heart valves.
Some possible explanations for the other choices are:
Choice A is wrong because the pericardium is the sac that surrounds the heart and consists of two layers: the fibrous pericardium and the serous pericardium.
Choice C is wrong because the myocardium is the thick middle layer of muscle that allows the heart chambers to contract and relax to pump blood to the body.
Choice D is wrong because epicardium is another name for the visceral layer of the serous pericardium that is fused to the heart and is part of the heart wall.