Karl Von Baer's Observations of Vertebrate Embryos Suggest That

Karl von Baer's observations of vertebrate embryos suggest that:

A) fish are unrelated to other vertebrates because they are the only vertebrates that develop gills.
B) fish, turtles, and mice are more closely related to one another than to either chickens or humans because they have substantial tails.
C) chickens and humans are closely related because they lack substantial tails.
D) all vertebrate species have similar genes for development, with some being active in some species and inactive in others.