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

the oceanic zone is typically defined as the area of the ocean lying beyond the continental shelf, but operationally is often referred to as beginning where the water depths drop to below 100 meters (328 feet), seaward from the coast to the open ocean.

explanation: