Which of the following usually accounts for the smallest percentage of leukocytes in a blood sample?

This is because it is an example of a positive feedback loop, which amplifies the change and moves the system away from its normal state.
A negative feedback loop is a mechanism that reverses a deviation from the set point and maintains homeostasis.
Choice A is wrong because increasing heart rate and force of contraction when blood pressure falls is a negative feedback loop that restores blood pressure to normal.
Choice B is wrong because secreting insulin after a meal to return blood sugar concentration toward normal is a negative feedback loop that regulates glucose levels.
Choice D is wrong because shivering when body temperature falls below normal is a negative feedback loop that increases heat production and raises body temperature.
Normal ranges for blood pressure are 90/60 mmHg to 120/80 mmHg, for blood glucose, are 70 mg/dL to 140 mg/dL, and for body temperature are 36.5°C to 37.5°C or 97.7°F to 99.5°F.

Monocytes are a type of agranulocytes, which are white blood cells that lack visible granules in their cytoplasm.
Agranulocytes also include lymphocytes, which are involved in adaptive immunity.
Choice A is wrong because basophils are a type of granulocytes, which are white blood cells that have granules in their cytoplasm.
Granulocytes also include neutrophils and eosinophils, which are involved in innate immunity.
Choice C is wrong because neutrophils are also a type of granulocyte.
Neutrophils are the most abundant white blood cells and are responsible for phagocytizing bacteria and fungi.
Choice D is wrong because eosinophils are also a type of granulocytes. Eosinophils are involved in allergic reactions and parasitic infections.
Normal ranges for white blood cells vary depending on age, gender, and health status, but generally, they are between 4,000 and 11,000 cells per microliter of blood.