Correct Answer: B

Rationale: The primary function of red blood cells, also known as erythrocytes, is to transport oxygen from the lungs to the body's tissues and organs. This is essential for cellular respiration and overall body functions. Red blood cells do not play a role in clotting blood, fighting infection, or carrying hormones. Choice A is incorrect because clotting blood is primarily done by platelets and other components of blood. Choice C is incorrect as fighting infection is a function mainly carried out by white blood cells. Choice D is incorrect because carrying hormones is primarily attributed to proteins like albumin and specific hormone-carrying proteins.

Correct Answer: B

Rationale: The correct answer is B: 'To break down food.' The stomach plays a crucial role in the digestive system by breaking down food using gastric acid and digestive enzymes. This process transforms the food into a semi-liquid mixture known as chyme, which is further digested in the small intestine. Choices A, C, and D are incorrect because the stomach does not primarily absorb nutrients, produce bile, or store waste. These functions are carried out by other organs in the digestive system such as the small intestine, liver, and large intestine, respectively.

Correct Answer: C

Rationale: The main function of the lymphatic system is to fight infections. It achieves this by filtering lymph, returning excess tissue fluid to the bloodstream, and aiding in the body's immune response. The lymphatic system is crucial in protecting the body against pathogens and maintaining overall health. Choices A, B, and D are incorrect because transporting oxygen, producing hormones, and transporting nutrients are functions performed by other systems in the body, like the respiratory, endocrine, and circulatory systems, respectively.

Correct Answer: A

Rationale: The correct answer is ADH (antidiuretic hormone), also known as vasopressin. ADH helps regulate water balance in the body by controlling the amount of water reabsorbed by the kidneys. When there is a need to conserve water, ADH levels increase, leading to more water reabsorption and concentration of urine. Insulin is involved in regulating blood sugar levels, not water balance. Cortisol is a stress hormone that helps regulate metabolism and immune response, not water balance. Thyroxine is a thyroid hormone that regulates metabolism, growth, and development, not water balance.

Correct Answer: B

Rationale: The correct answer is the Adrenal gland. The Adrenal glands, situated on top of the kidneys, are responsible for producing adrenaline. Adrenaline is a hormone that prepares the body for the fight-or-flight response during stress. Choice A, the Thyroid gland, is responsible for producing hormones that regulate metabolism, not adrenaline. Choice C, the Pituitary gland, regulates many of the body's functions by producing various hormones but is not responsible for adrenaline production. Choice D, the Pineal gland, produces melatonin, a hormone that regulates sleep-wake cycles, and is not responsible for adrenaline production.