支付除草费用——只要自己给院子割草，每个月你就能节省150美元，得到有益身心的锻炼，说不定还能晒出（你想要的）黑呢。
Pay for Lawn Service – You could save $150 a month, get some healthy exercise and maybe even a bit of a tan just by mowing your own yard.
而驯鹿呢，虽然它们没有昼夜节律钟，其褪黑激素水平仍然会在黑暗的时候上升，光亮的时候下降，从而使它们的昼夜分点达到理想状态，进而与年生物钟同步。
In reindeer, even if they're missing a circadian clock, melatonin levels still spike when it's dark and drop when it's light, making the equinoxes an ideal time to synchronize their annual clocks.
黑巧克力里的什么物质在使然呢？
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