An adolescent who regularly engages in strenuous physical activity has mild pain along the medial tibia, which is now developing earlier in the exercise period. The pain is over a 5- to 15-cm area of the posterior tibialis muscle body, just medial to the medial tibia, but not over the bone. Which is the most likely diagnosis?

Correct Answer: D

Rationale: Shin splints cause pain along the medial tibia from muscle overuse, fitting the activity-related pattern described.

Correct Answer: B

Rationale: Hypokalemia causes polyuria, reduced ammonia production, and renal damage, but urinary retention is not a feature; it's more associated with hyperkalemia.

Correct Answer: D

Rationale: Severe anemia increases anion gap via lactic acidosis; others cause normal anion gap acidosis.

Correct Answer: B

Rationale: Water needs increase by 10-15% per °C above 38 °C due to increased insensible losses.