Sex organs of males and females are involved in reproduction, ensuring the continuation of the genetic material.
Gonads do not produce all cells.
Gonads do not produce interstitial cells either.
Therefore, options A, B and D are not correct because they have partially incorrect answers.
The main function of male and female gonads is to produce gametes and hormones. In males, the gonads are called testes and they produce sperm cells (male gametes) and hormones like testosterone. In females, the gonads are called ovaries and they produce ova (or eggs) and also secrete hormones like estrogen. The hormones produced by gonads give rise to secondary sexual characteristics like beards in men and breasts in women.
Therefore, option (C) is correct.