Correct Answer: B

Rationale: The main function of the immune system is to protect the body from infections by identifying and destroying pathogens like bacteria and viruses. It plays a crucial role in maintaining overall health and preventing illnesses. Choice A is incorrect because hormone production is primarily handled by the endocrine system, not the immune system. Choice C is incorrect as waste removal is mainly performed by the excretory system, not the immune system. Choice D is incorrect as regulating body temperature is primarily the role of the thermoregulatory system, not the immune system.

Correct Answer: B

Rationale: Vitamin A is the correct answer. It is essential for maintaining healthy skin and vision, especially in low-light conditions. Vitamin A helps in the production of retinal pigments necessary for vision in dim light and supports skin health by promoting cell turnover and repair. Choice A, Vitamin C, is important for the immune system and collagen production but is not specifically known for maintaining skin and vision health. Choice C, Vitamin D, is crucial for bone health and immune function but is not directly related to skin and vision health. Choice D, Vitamin K, is necessary for blood clotting and bone health but does not play a significant role in maintaining healthy skin and vision.

Correct Answer: B

Rationale: The correct answer is B: 'They secrete chemicals into the blood.' Endocrine glands release hormones directly into the bloodstream to regulate various body functions. This process helps in maintaining homeostasis and coordinating different physiological processes within the body. Choice A is incorrect as endocrine glands do not absorb chemicals from the blood; instead, they release hormones. Choice C is incorrect as endocrine glands do not filter chemicals from the blood; they secrete hormones. Choice D is incorrect as endocrine glands do not absorb chemicals from the lymphatic system; they release hormones into the bloodstream.

Correct Answer: A

Rationale: The cochlea, located in the inner ear, is responsible for detecting sound waves and converting them into neural signals that are sent to the brain for processing. It plays a crucial role in the process of hearing by translating mechanical vibrations into electrical signals that the brain can interpret as sound. The semicircular canals (Choice B) are responsible for balance and detecting head movements, not hearing. The ossicles (Choice C) are three tiny bones in the middle ear that transmit sound vibrations from the eardrum to the cochlea. The Eustachian tube (Choice D) helps equalize pressure between the middle ear and the atmosphere, but it is not directly involved in the process of hearing.

Correct Answer: A

Rationale: The correct answer is 'Larynx.' The larynx is indeed located in the upper respiratory system alongside the pharynx. Positioned below the pharynx and above the trachea, the larynx is crucial for breathing and sound production. The trachea and bronchi are part of the lower respiratory system and are situated below the larynx, making them incorrect choices in this context.