Consider these lines: "Many people with sickle-cell anemia, and the particular genetic mutation that causes it, die at an early age. Despite the negative evolutionary effects associated with this genetic mutation, the sickle-cell gene remains relatively common among people of African descent. In parts of Africa where malaria is prevalent, having the sickle-cell mutation does provide health benefits for carriers." Based on the quoted lines, why does the gene stay common despite its costs?

1. The quoted lines pose a puzzle: the mutation kills early, yet the gene stays relatively common. 2. The resolution arrives in the final sentence: where malaria is prevalent, carriers gain a health benefit. 3. That benefit offsets the cost, so the gene persists in exactly those places, which is option A. 4. Option C overreaches from one disease, malaria, to every tropical disease, a scope the quoted lines never claim. 5. Option B contradicts the opening sentence about early deaths, and option D contradicts the whole selection logic. _Source: OpenStax Psychology 1e (CC BY 4.0), Ch 3 "Biopsychology", section 3.1 Human Genetics_