Correct Answer: C

Rationale: Merkel cells are specialized touch receptors located in the epidermis of the skin. Their primary function is to perceive light touch and pressure. They play a crucial role in the sensory perception of touch stimuli. Option A, melanin production, is incorrect because Merkel cells are not involved in producing melanin. Option B, temperature sensation, is incorrect as Merkel cells are not specialized for sensing temperature. Option D, immune defense, is also incorrect as Merkel cells do not have a role in immune defense mechanisms.

Correct Answer: C

Rationale: Friction is a force that opposes motion. When two surfaces are in contact, friction acts in the opposite direction to the motion or the potential motion between the two surfaces. It resists the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. Friction hinders or prevents motion rather than promoting it. Choices A, B, and D are incorrect as they suggest that friction increases, accelerates, or creates motion, which is inaccurate. The correct definition of friction is that it opposes motion, making choice C the most appropriate option.

Correct Answer: D

Rationale: A) Carbohydrates: Carbohydrates require digestion by enzymes in the mouth, stomach, and small intestine before they can be broken down into simple sugars for absorption. B) Proteins: Proteins need to be broken down into amino acids by stomach acid and digestive enzymes in the stomach and small intestine before they can be absorbed. C) Fats: Fats require bile from the gallbladder to emulsify them into smaller droplets for enzymes to break them down into fatty acids and glycerol for absorption. D) Vitamins: Vitamins are organic compounds that are already in a form that can be readily absorbed by the body without extensive digestion. They are absorbed directly into the bloodstream from the small intestine and do not require significant breakdown before absorption.

Correct Answer: C

Rationale: When a ball is thrown horizontally, its horizontal velocity remains constant throughout its motion. The horizontal distance traveled by the ball is determined by the horizontal velocity and the time taken to hit the ground. In this case, the horizontal distance is calculated as distance = velocity time. Since the horizontal velocity is 10 m/s, the horizontal distance traveled by the ball is 10 m/s time. The time taken to hit the ground is determined by the vertical motion, which is independent of the horizontal velocity. Therefore, without knowing the height of the cliff, we can still determine the horizontal distance traveled by the ball. The horizontal distance is solely dependent on the horizontal velocity and the time of flight, which are not influenced by the height of the cliff. Hence, the correct answer is 30 m. Choice A, 10 m, is incorrect as it does not consider the time of flight. Choice B, 20 m, is incorrect as it does not account for the constant horizontal velocity. Choice D, 'Cannot be determined without knowing the height of the cliff,' is incorrect because the horizontal distance can be calculated independently of the height of the cliff.

Correct Answer: C

Rationale: The simple columnar epithelium lining the small intestine is crucial for absorption. This type of epithelium is specialized for absorption due to its tall and closely packed cells, which increase the surface area available for nutrient absorption. The primary function of the small intestine is to absorb nutrients from digested food, and the simple columnar epithelium's structure aids in this process by providing a large surface area for absorption. Choices A, B, and D are incorrect because movement, support, and insulation are not primary functions associated with the simple columnar epithelium in the small intestine. While these functions are essential in other tissues or organs, absorption is the key role of the simple columnar epithelium in the small intestine.