According to embryology, why do fish and birds have a common ancestor?
they both have embryos with gill slits and tails.

they both have embryos with traits that eventually disappear.

they both have embryos that develop into adults.

they both have embryos that form from a fertilized egg.

Both fish and bird embryos exhibit gill slits and a tail.

Explanation:

According to embryology, all vertebrates exhibit similar traits and structures at their embryonic stage. It becomes very difficult to differentiate between the embryos of a fish, and that of a bird, or embryo of a fish, and a human. These traits, however, disappear, as the case may be, as the embryo develops into an adult. For example, in the case of the embryo of a fish, and a bird, both shows gills slits at their respective embryonic stage. However, the gill slits in fish develop into gills, whereas in the case of birds, it disappears as the embryo develops into an adult.

a=c and then d= c because of the band so you get ac/dc and you add them together you get sound waves