The following drug can cause rickets in children by interfering with vitamin D action:

Correct Answer: A

Rationale: The correct answer is A: Tetracycline. Tetracycline can cause rickets in children by binding to calcium in bones, inhibiting bone growth. This interference with vitamin D action leads to impaired calcium absorption. Digoxin, Phenytoin, and Ciprofloxacin do not interfere with vitamin D metabolism or calcium absorption, ruling them out as potential causes of rickets in children.

Correct Answer: C

Rationale: The correct answer is C: Intravenous calcium gluconate. Tetany is caused by low levels of calcium in the blood. Calcium gluconate is the appropriate treatment as it quickly and effectively raises blood calcium levels. Diazepam (A) is a muscle relaxant, vitamin D (B) is used for bone health, and calcitonin (D) is used to regulate calcium and phosphate levels in the body, but they are not the primary treatment for tetany.

Correct Answer: A

Rationale: The correct answer is A (1-2 months) because fertility typically returns quickly after stopping the combined estrogen-progestin contraceptive pill. Estrogen and progestin hormones are quickly metabolized and cleared from the body, allowing the menstrual cycle to resume within a month or two. Choice B (4-6 months) is incorrect as fertility usually returns sooner. Choice C (6-12 months) is also incorrect as it is an extended timeframe for fertility to return. Choice D (Uncertain period) is incorrect as there is a general understanding of the timeline for fertility to return after stopping the pill.

Correct Answer: A

Rationale: The correct answer is A: Long acting progestin. Injectable hormonal contraceptives typically contain progestin alone, as it suppresses ovulation and thickens cervical mucus. Estrogen is not commonly used in injectable contraceptives due to its higher risk of side effects like blood clots. Chorionic gonadotropin is not a component of injectable contraceptives and is typically used in fertility treatments. Therefore, choice A is correct as it aligns with the mechanism of action and formulation of injectable hormonal contraceptives.

Correct Answer: C

Rationale: The correct answer is C because progestin and estrogen work together to suppress ovulation by inhibiting the release of gonadotropins. Progestin thickens cervical mucus, making it hostile to sperm, while estrogen stabilizes the endometrium. Choices A and B are incorrect because the hormones don't block each other's side effects. Choice D is incorrect because it oversimplifies the mechanism of action.