Young boys at puberty start growing facial hairs. This is an example of:

The correct option is B Secondary sexual character

• The secondary sexual characters refer to sex-specific characters of males and females.
• Female secondary sexual characters are a feminine pattern of body hair and fat distribution.
• Male secondary sexual characters include stimulated synthesis of structural proteins of skeletal muscles and bones, voice deepening, growth of facial, axillary and pubic hairs etc.

Therefore, the correct answer is option A.