Multiple choice Which of the following develops into the placenta? Umbilical cord Inner cell mass of the blastocyst Decidua Myoblast cells Trophectoderm Reveal answer Fill a bubble to check yourself E Correct answer Explanation The developing embryo has two main populations of cells: an inner cell mass and a trophectoderm. The trophectoderm cells lie at the outer surface of the developing embryo and will become the placenta.