The correct option is C Neurulation
Metamorphosis is the process by which an organism changes its form or habits during normal development after embryonic stage.
Gastrulation is the process, where there are cell movements, which result in the reorganization of the embryo from blastula to gastrula.
Neurulation is the process of folding in the embryos of vertebrates, where there is the transformation of neural plate into the neural tube. This process induces the formation of the central nervous system.
Invagination is the infolding of one part within another part and it involves the morphogenetic processes by which an embryo takes form and is the initial step of gastrulation.
Thus, the correct answer is the option (C), 'Neurulation'.