Which has been observed in the study of embryology? A. Species whose embryos have similar traits rarely have a common ancestor.
B. Species whose embryos have similar traits always have similar body forms as adults.
C. All traits present in early embryos remain throughout development.
D. Some traits in certain embryos disappear as the embryo develops.

D. Some traits in certain embryos disappear as the embryo develops

Explanation:

I don't know how I would explain it, but I can list some of the things that disappear such as...  Gill slits, and tails. Hope this helped :D

primary succession begins with a bare rock and ends with a forest secondary succession begins after a natural disaster where there is a temporary setback after a forest fire or local destruction, but the surrounding area can fill in