The correct option is A the sixth month of pregnancy
After implantation, the inner cell mass of the developing embryo starts differentiating into three germ layers. The outer layer is called the ectoderm and the inner layer is called the endoderm. And in between these two, there is the mesoderm. These three germ layers give rise to all tissues and organs of the body.
Human pregnancy lasts 9 months. During this gestation period, most of the major organs and tissues of the body develop. After the first month of the pregnancy, the heart is formed in the embryo. The sound of the heart of the foetus is the first sign of the growing foetus.
External genital organs, limbs, digits are formed in the second month of the pregnancy. Hair on the head and movement of the foetus is observed in the fifth month.
By the end of the sixth month (second trimester) the body is covered with the hair, eyelids separate and eyelashes are formed.
By the eighth month of pregnancy, the testes in the male foetus descend into the scrotum.
And as gradually the gestation period is approaching an end, the foetus grows fully in the ninth month and is ready for birth.