Correct Answer: A

Rationale: Certain young people might be underweight because they are growing in height faster than they are gaining weight. During periods of rapid growth, the body's energy requirements are primarily directed towards height growth rather than weight gain, resulting in some individuals being underweight despite consuming sufficient calories. Choice B is incorrect because the question focuses on reasons related to growth rather than diet composition. Choice C is incorrect as it suggests overeating rather than the specific growth-related issue of height surpassing weight gain. Choice D is incorrect as it addresses nutritional variety rather than the growth dynamics affecting weight.

Correct Answer: D

Rationale: Progesterone initiates the preparation of the endometrium of the uterus for pregnancy. It promotes the growth of blood vessels and glands in the endometrial lining, making it conducive for implantation and supporting early pregnancy. While estrogen helps in thickening the endometrium, it is progesterone that plays a crucial role in preparing it for pregnancy. FSH (Follicle-stimulating hormone) is involved in stimulating ovarian follicles, not directly in preparing the endometrium. LH (Luteinizing hormone) triggers ovulation but does not primarily prepare the endometrium for pregnancy.

Correct Answer: D

Rationale: The correct answer is D. The skull is superior to the spinal cord, meaning it is located above the spinal cord in anatomical position. Superior in anatomy refers to a structure being positioned higher or above another structure in the body. Choices A, B, and C are incorrect because they refer to different directional relationships. Anterior means in front of, posterior means behind, and lateral means to the side. In this case, the relationship between the skull and the spinal cord is based on a superior-inferior orientation.

Correct Answer: D

Rationale: The correct answer is D, 'Production of antibodies.' Antibodies are generated as part of the specific immune response, which targets specific antigens. Nonspecific immune responses, such as inflammation, vasodilation, and histamine release, are general defense mechanisms aimed at combating various pathogens. Inflammation is a localized response to infection or injury, vasodilation increases blood flow to the affected area, and histamine release triggers inflammatory responses. It's vital to differentiate between nonspecific responses that provide immediate, general protection and specific responses designed to tackle particular threats.

Correct Answer: B

Rationale: The urinary system, specifically the kidneys, is primarily responsible for regulating electrolytes in the body by filtering and excreting excess electrolytes, such as sodium, potassium, and chloride, through urine. The kidneys play a crucial role in maintaining the body's electrolyte balance, which is essential for various bodily functions and overall health. The endocrine system regulates hormones, the lymphatic system is involved in immunity, and the nervous system controls communication in the body. Therefore, the correct answer is B, the urinary system, as it directly handles electrolyte regulation by adjusting their excretion levels.