Correct Answer: D

Rationale: The integumentary system, which includes the skin, performs various functions like protecting internal tissues from injury, waterproofing the body, and helping regulate body temperature. The function of returning fluid to the blood vessels is primarily associated with the lymphatic system, not the integumentary system. The skin contributes to fluid balance by regulating sweating and preventing excessive water loss, but it does not directly return fluid to the blood vessels, making this the correct answer. Choices A, B, and C are functions directly related to the integumentary system and are essential for maintaining the body's overall health and well-being.

Correct Answer: C

Rationale: The term 'proximal' means situated close to the point of attachment or the center of the body, such as close to the trunk. In anatomical terms, proximal is used to describe locations that are closer to the body's center or point of reference. 'Superficial' refers to something situated near the surface, 'sagittal' refers to a plane that divides the body into left and right portions, and 'distal' refers to a position away from the center or point of reference. Therefore, 'proximal' is the correct term to indicate a position close to the trunk of the body.

Correct Answer: D

Rationale: The given scenario presents multiple possible explanations for the decline in the insect population with the introduction of a particular plant. It could be due to the plant being toxic to the insect (Option A), competing with and driving out plants that the insect feeds on (Option B), or the decline could be coincidental with the plant introduction as the insect population was already decreasing (Option C). Without further investigation and evidence, it is not possible to definitively determine which explanation is correct. Therefore, all of these possibilities may be true, and thorough investigation is necessary to reach a conclusive conclusion.

Correct Answer: D

Rationale: The iris is the colored part of the eye that determines the eye's color. Melanin is not present in the iris, unlike hair, nails, and skin. Melanin gives color to hair, nails, and skin, but not to the iris. Therefore, the correct answer is the iris (Choice D). Choices A, B, and C contain melanin and are incorrect.

Correct Answer: A

Rationale: The most logical reason for some of the plants dying with the salt solution could be that salt caused the plants to begin to dry up, leading to their death. Excessive salt can disrupt the osmotic balance within plants, causing dehydration and ultimately death. Salt can create a hypertonic environment, drawing water out of plant cells and causing wilting and damage. Therefore, it is reasonable to assume that the presence of salt could have dried out some of the plants and caused them to die. Choices B and C are incorrect as the scenario presented indicates that the salt had a negative impact on the plants, causing some to die. Choice D is also incorrect as there is a valid reason provided for the plants dying due to the salt solution.