The Earliest Large,mobile Life Forms That May Have Been Able

The earliest large,mobile life forms that may have been able to live and reproduce on land were amphibians.Most amphibians lay eggs.Why would laying eggs have been a logical step in the evolution of mobile life forms from sea to land?

A) Eggs have hard shells, which would have prevented predatory dinosaurs and early flying birds/mammals from smelling and eating the tiny new amphibian life.
B) Egg shells are opaline, which could have been dissolved by the growing reptile embryos to produce chemicals to create calcium carbonate skeleton as they grew.
C) Eggs contained chemically stable solutions from which growing life forms could reliably extract nutrients, in a manner resembling fish eggs laid in seas and oceans.
D) Egg shells would have provided sufficient protection from solar radiation to allow an embryo to grow without damage.