Question

what factor is contributing the most to the decline of coral reefs in oceans?
increased ocean acidity
reduced harmful radiation
cooler ocean temperatures
decreased ocean pollution

Explanation:

Coral reef decline is largely due to ocean acidification (from increased CO₂ absorption), which harms coral skeletons. Reduced radiation, cooler temps, and decreased pollution would not cause decline (they’d help or are irrelevant). So "Increased ocean acidity" is correct.

Answer:

A. Increased ocean acidity