43. Which of the following statements concerning embryonic developments of humans is correct? (A) A fertilized egg undergoes many rounds of cell division to form an early embryo called blastocyst when it arrives at the uterus. (B) Trophoblast cells eventually forms the three germ layers at the end of gastrulation. (C) Adrenal cortex is developed from ectoderm. (D) Epidermis and its derivatives such as hair follicles are derived from endoderm.