Which of the following statements are true for human embryonic development?

a) Placenta is the structural and functional unit between foetus and maternal body.

b) Placenta is connected to embryo through an umbilical cord.

c) Stem cells are present in inner cell mass which have the potency to give rise to all the tissues and organs.

d) hCG, hPL, estrogens and progestogens are secreted only by placenta.

e) All fertilisations lead to implantation.

Choose the most appropriate answer from the options given below.