Which of the following is the most appropriate statement defining infertility?

• A
  Couple is unable to produce children in spite of unprotected sexual co-habitation even after two years.
• B
  It is the inability to produce a viable offspring and is always due to defects or abnormalities in the female partner.
• C
  Infertility is due to immature sex organs.
• D
  Infertility cannot be helped by $ART$.