The ultra violet (UV) rays that cause suntans also cause a kind of chemical, called endorphins, to be released into the blood.
造成皮肤晒黑的紫外线，也会造成一种称为脑内啡的化学物质被释放进血液中。
The ultra violet (UV) rays that cause suntans also cause a kind of chemical, called endorphins, to be released into the blood.
造成皮肤晒黑的紫外线，也会造成一种称为脑内啡的化学物质被释放进血液中。
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