The events after fertilization occur in the following sequence:

Step 1: Formation of Morula (D)
After fertilization, the zygote undergoes repeated mitotic divisions (cleavage).
It forms a solid ball of 8–16 blastomeres, known as the morula.

Step 2: Formation of Blastocyst (C)
The morula develops into a blastocyst.
In the blastocyst:
The outer layer differentiates into the trophoblast.
The inner group of cells forms the inner cell mass (ICM), which develops into the embryo.

Step 3: Implantation (A)
Around 6–7 days after fertilization, the blastocyst attaches to and becomes embedded in the endometrium of the uterus.
This process is called implantation.

Step 4: Formation of Chorionic Villi (B)
After implantation, the trophoblast develops finger-like projections called chorionic villi.
These villi help form the placenta, enabling the exchange of nutrients, oxygen, and waste products between the mother and the developing fetus.