During the course of development, cells in various regions of embryo become variable in morphology and eventually perform diverse functions. This process is known as

The role of placenta is

The persistence of corpus luteum during pregnancy is due to a hormone known as

The hormone released from placenta is

Assertion : During fertilization only head of spermatozoa enters egg.

Reason : If several spermatozoa hit the egg at same time, all can enter the egg.