A parietal layer of a serous membrane lines cavities, whereas a visceral layer of a serous membrane covers organs.

Correct Answer: B

Rationale: In serous membranes, the parietal layer lines the cavities, providing support and protection, while the visceral layer covers the organs, reducing friction and allowing them to move freely. Therefore, the correct answer is 'lines cavities; covers organs.' Choices C and D are incorrect because serous membranes do not secrete mucus; instead, they secrete a watery serous fluid. Choice A is incorrect as it reverses the functions of the parietal and visceral layers in relation to organs and cavities.

Correct Answer: B

Rationale: The correct answer is 'the age of her eggs.' As women age, the quality of their eggs decreases, leading to a higher risk of chromosomal abnormalities and infertility. This decline in egg quality is why advanced maternal age is associated with a higher risk of certain pregnancy complications. Choices A, C, and D are incorrect because the primary concern in this context is related to the age-related changes in a woman's eggs, not sperm, diabetes risk, or cholesterol levels.

Correct Answer: C

Rationale: Wrinkled and sagging skin is primarily caused by the loss of subcutaneous fat and reduced levels of elastin and collagen in the skin. Choice A is incorrect as drinking too much water does not lead to wrinkled and sagging skin. Choice B is incorrect because heredity alone does not cause this condition. Excess subcutaneous fat, as mentioned in Choice D, can contribute to a different skin appearance, such as puffiness, but not wrinkled and sagging skin.

Correct Answer: C

Rationale: The correct answer is 'impaired cell division and the ability to break down and recycle worn cell parts.' Aging at the cellular level involves reduced efficiency in cell division and the breakdown/recycling of cellular components, leading to functional decline. Choices A, B, and D are incorrect because they involve external physical manifestations or organ-specific issues rather than cellular-level changes associated with aging.

Correct Answer: D

Rationale: The correct answer is 'never having smoked.' Research suggests that one of the common characteristics among centenarians is that they have never smoked. Smoking is a well-known risk factor for various diseases and can significantly reduce lifespan. Choice A, 'a high level of exercise throughout life,' is not a universal characteristic among centenarians, although exercise can contribute to a healthy lifestyle. Choice B, 'long-lived relatives,' while genetics can play a role in longevity, not all centenarians have long-lived relatives. Choice C, 'following the Mediterranean diet,' is a healthy dietary choice but not a defining characteristic shared by all centenarians.