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12 years ago
 In placental mammals, the yolk sac   
A) differentiates into the placenta.
B) transfers nutrients from the yolk to the embryo.
C) becomes a fluid-filled sac that surrounds and protects the embryo.
D) produces blood cells that then migrate into the embryo.
E) stores waste products from the embryo until the placenta develops.
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12 years ago
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