The correct answer is (B) A young woman who has reached age 18 and is making her first appearance at a formal social function; one her is having her formal introduction to society; one making her debut (coming out) into society.

Examples of use:

• The formal occasion at which a debutante is presented to society is known as her debut.
  
  
• When a woman became a debutante, it was understood that she was eligible for marriage.