母乳不是维生素d的充足来源：我们更适宜在接近赤道的地方生活。
Breast milk is not an adequate source: we are designed to live nearer the equator.
事实上，气球并非是一个完美的球体，北极地区要比赤道地区更加接近地心，两地之间的这一差距大概是在数公里。
The Earth isn't completely spherical - land at the North Pole is a number of kilometres nearer to the core of the planet than land at the Equator.
在每一年的春分点上，太阳横跨着地球上的赤道，使得地球上大部分地区的白天和夜晚的时间接近相等。
At each equinox, the sun crosses the Earth's equator, making night and day of approximately equal length on most of the planet.
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