________(make)naturallybytheskinwhenexposedtosunlight,v...

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________ (make) naturally by the skin when exposed to sunlight, vitamin D is needed for healthy bones, teeth and muscles.

Made　句意：当暴露在阳光下的时候，维生素D自然就在皮肤中形成了，它是健康的骨头、牙齿和肌肉所需要的。vitamin D和make之间是被动关系，故填Made。