Key Concept: Water-soluble vitamins leach out wherever food sits directly submerged in water during cooking.
Why it's correct: Steaming cooks vegetables using vapor without submerging them, so vitamins like C and B-complex stay in the food instead of leaching into the cooking water.
Why others fail: Boiling still submerges food (nutrient loss into water), deep frying uses high heat/oil that degrades nutrients, and microwaving can cook unevenly — none preserves nutrients as reliably as steaming.