每日背誦第五期63
Cells in the human skin produce a substance called melanin. When sunlight hits the skin, more melanin is produced. Melanin darkens the skin and is the cause of suntan. Most people tan evenly all over the body, but some people tan just in spots. These little islands of suntan are the cause of freckles.
人類皮膚里的細(xì)胞產(chǎn)生一種物質(zhì)叫黑色素。當(dāng)陽光照到皮膚，會產(chǎn)生更多的黑色素。黑色素使皮膚變黑是人被曬黑的原因。大多數(shù)人是整個身體均勻的曬黑，可一些人是局部曬黑。這些小黑斑就形成了雀斑。
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