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.

This type of blood cell is a granulocyte that has a bi-lobed nucleus and red granules in the cytoplasm.

Eosinophils are involved in allergic reactions and parasitic infections.
Choice A is wrong because basophils are granulocytes that have a lobed nucleus and dark blue or purple granules in the cytoplasm.
Basophils are involved in inflammatory responses and histamine release.
Choice B is wrong because lymphocytes are agranulocytes that have a large round nucleus and a thin rim of cytoplasm.
Lymphocytes are involved in immune responses and produce antibodies.
Choice D is wrong because monocytes are agranulocytes that have a kidney-shaped nucleus and a pale blue cytoplasm.
Monocytes are involved in phagocytosis and tissue repair.
Choice E is wrong because neutrophils are granulocytes that have a multi-lobed nucleus and pale pink granules in the cytoplasm.
Neutrophils are involved in bacterial infections and inflammation.

The pulmonary circuit sends oxygen-poor blood to the lungs, where it is oxygenated and returned to the heart.
This is distinguished from the systemic circuit, which sends oxygen-rich blood to the tissues and returns oxygen-poor blood to the heart.
Choice A is wrong because it confuses the pulmonary circuit with the systemic circuit. The pulmonary circuit does not send blood to the tissues but to the lungs.
Choice B is wrong because it only describes part of the pulmonary circuit.
The pulmonary circuit sends oxygen-poor blood to the heart, but only after it has been oxygenated in the lungs.
Choice C is wrong because it confuses the pulmonary circuit with the systemic circuit. The pulmonary circuit does not bring blood from the tissues but from the heart.