The cardiac reserve is

Correct Answer: B

Rationale: Cardiac reserve is the difference between maximum cardiac output (CO) during exercise and resting CO. Resting CO = 84 × 0.06 = 5 L/min; exercise CO = 13 L/min. Reserve = 13 - 5 = 8 L/min. '8 L/min,' is correct, per cardiovascular physiology (e.g., Berne & Levy). Choice A is exercise CO, not reserve. Choice C and D misalign. B's calculation fits, making it the answer.

Correct Answer: C

Rationale: Oxytocin, from the posterior pituitary, triggers milk ejection by contracting myoepithelial cells in the breast. 'Oxytocin,' is correct, per physiology texts like Costanzo, distinct from milk production. 'Progesterone,' supports pregnancy, not ejection. 'Prolactin,' stimulates milk synthesis. 'Oestrogen,' aids breast development. Oxytocin's specific let-down reflex role makes C the accurate answer, critical in lactation.

Correct Answer: C

Rationale: Vitamin C (ascorbic acid) prevents scurvy by aiding collagen synthesis, essential for connective tissue. 'Vitamin C,' is correct, per nutrition texts like Shils, reversing symptoms like bleeding gums. 'Vitamin A,' supports vision. 'Vitamin B,' is a group, none specific to scurvy. 'Vitamin D,' aids bone health. Vitamin C's historical link to scurvy prevention, notably in sailors, makes C the accurate answer.

Correct Answer: C

Rationale: The small intestine averages 7 meters in adults, varying (6-7 m). '7 m,' is correct, per anatomy (e.g., Tortora), spanning duodenum, jejunum, and ileum. '3 m,' is too short. '5 m,' underestimates. '9 m,' exceeds typical length. The 7 m standard reflects its absorptive expanse, making C the accurate answer.

Correct Answer: B

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.