钙是生成强壮骨骼的必须营养成分，并保持骨骼健康。
Calcium is an essential nutrient for building strong bones and keeping them healthy.
但是维生素是人们每天摄入的必须营养；没有办法在临床研究中全部去除它们来观察效果。
But vitamins are essential nutrients that people ingest in their daily diets; there is no way to withhold them altogether from research subjects.
可是，如果海面水温较高(例如在厄尔尼诺期间)，深层海水就无法上流，从而大大阻断了这些生命必须营养的正常循环。
However, when surface waters are warm (as during an el ni? O), they do not allow the colder, deeper currents to upwell and effectively block the flow of life-sustaining nutrients.
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