Embryology is the study of the development of organisms including the formation of gametes, fertilization, and embryos and fetuses development until the moment of birth.
On the other hand, comparative anatomy refers to the study and comparison of the anatomies of different species to look at their similarities and differences and is helpful for finding evidence of common descent.
Comparative embryology is a branch of embryology that is similar to comparative anatomy because it compares the embryos of different species to study how are they related.
Given that the question says that " It is a great way to study animal development, but it is not a proof of evolution.", then it should be referring to embryology in general, and that would be the right answer.