When a pregnant woman ingests toxins such as alcohol and nicotine, the embryo is put at risk because these toxins can

1) diffuse from the mother's blood into the embryo's

blood within the placenta

2) enter the embryo when it eats

3) transfer to the embryo since the mother's blood

normally mixes with the embryo's blood m the placenta

4) enter the uterus through the mother's navel