External or accessory or secondary sexual characters first appear in

The correct option is A Puberty
External or accessory or secondary sexual characters are the changes that occur in male and female during puberty due to the high level of male and female hormones i.e., testosterone in males and estrogen in females. The examples of secondary characters are the growth of beards, moustaches in males and growth of breasts, broadening of the pelvis, etc in females.

So, the correct option is B.