The journal editors say, "If internal and international migrants comprised a nation, it would be the third most populous country in the world,just after China and India."
VOA: special.2011.07.06
It's this tube-like structure, which is made of many, many epithelial cells all directly adjacent to each other, is what separates the outside world from our internal bodies.
这些管状结构,也是由许许多多上皮细胞,互相连接而成的,它使体内和体外,区分开来
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