他说：“化石记录一再证实现代胎盘类哺乳动物的起源是在白垩纪-早第三纪分界点的时候或那之后。

“The fossil record continues to show that the origin of modern placental mammals postdates or is at the Cretaceous-Paleogene boundary, ” he said.

youdao

其实所谓的人胎素并不是指一个单一的特定物品名称，也不是特定物品的通用名，而是胎盘类制品的总称。

Actually, the so-called human fetal hormon doess not mean the name of a single specific item, also not the generic names of specific items.

youdao

史密斯博士说这些虱子不会在他的系统树上出现，除非它们转变成寄生在胎盘类哺乳动物身上的物种，而大多数虱子不会经常变换宿主。

These lice would not show up in his tree, Dr. Smith said, unless they had been able to transfer to the placental mammalian species, and most lice do not regularly switch hosts.

youdao