Correct Answer: D

Rationale: The correct answer is D. The immune system's primary function is to help the body avoid, detect, and eliminate infections. It does so by recognizing and responding to harmful pathogens, such as bacteria and viruses, to maintain the body's health and well-being. Choices A, B, and C are incorrect because the immune system is not controlled by the hypothalamus, its main role is not to filter toxins out of the blood, and while it can stimulate the production of certain immune cells, it does not directly stimulate the production of blood cells in response to infections.

Correct Answer: D

Rationale: The correct answer is D. The primary function of the endocrine system is to maintain homeostasis. Homeostasis refers to the stable internal conditions of the body, including body temperature, blood pH, and glucose levels. The endocrine system achieves this by releasing hormones that regulate various physiological processes and help keep the body's internal environment in balance. Choices A, B, and C are incorrect because while the endocrine system does influence heart rate, electrolyte and water balance, and respiration to some extent, its primary role is to regulate homeostasis by releasing hormones.

Correct Answer: C

Rationale: The rectum is part of the digestive system, not the genitourinary system. The genitourinary system comprises organs involved in reproduction and urine formation and excretion, such as the kidneys, urethra, and bladder. Choices A, B, and D are all components of the genitourinary system. The kidneys filter blood and produce urine, the urethra is a tube that carries urine from the bladder out of the body, and the bladder stores urine before it is excreted.

Correct Answer: D

Rationale: Density is an intensive property because it does not depend on the amount of matter present. Intensive properties are independent of the quantity of the substance and remain constant regardless of the size or amount of the sample being measured. Mass, weight, and volume are extensive properties that depend on the amount of substance present. Mass and weight change with the amount of matter, while volume changes as the quantity of the substance changes. Therefore, they are not considered intensive properties.

Correct Answer: C

Rationale: White blood cells, specifically B lymphocytes or B cells, are responsible for producing antibodies as part of the immune response. When the body encounters foreign substances (antigens), B cells are activated to differentiate into plasma cells, which then produce antibodies to target and neutralize the antigens. Platelets are involved in blood clotting and not in antibody production. Red blood cells are primarily responsible for carrying oxygen in the blood and do not produce antibodies. Plasma cells are actually differentiated B cells that produce antibodies, but the question asks for the blood component responsible for the production of antibodies, which is the white blood cells.