Many animals feed their newly born babies on milk from the mothers' own bodies.It's used instead of the blood that carries food to the babies before they were born.那个（It's used instead of the blood )啥意思

Many animals feed their newly born babies on milk from the mothers' own bodies.It's used instead of the blood that carries food to the babies before they were born.那个（It's used instead of the blood )啥意思
Many animals feed their newly born babies on milk from the mothers' own bodies.It's used instead of the blood that carries food to the babies before they were born.那个（It's used instead of the blood )啥意思

Many animals feed their newly born babies on milk from the mothers' own bodies.It's used instead of the blood that carries food to the babies before they were born.那个（It's used instead of the blood )啥意思
instead 是“而不是”的意思.it's.blood意思说“而不是通过血液”.整句意思说“许多动物是用自己的奶来喂养刚出生孩子而不是通过（在他们还没出生时给他们运输营养的）血液来喂养

许多动物用乳汁哺育新生儿，但是在新生儿出生前是血液代替乳汁来给它们供给食物。 括号里那个就是“它（指乳汁送养）过去是被血液所代替的”