A fetus is more developed than an embryo. So the last answer would be correct.
Through the ambilical cord
I'd say that the mechanism which might keep Rana aurora and Rana boylii from mating is B. temporal isolation, since their breeding seasons do not occur at the same time.
It is not anatomical isolation, since they are both frogs. It is not geographic isolation, since they meet in California. It is not behavioral isolation since they both have breeding seasons.