In humans, clear sex differentiation does not occur at fertilization. It becomes evident after the second month of gestation. Which of the following statements describes the first event of sex differentiation in human embryos?
A) production of testosterone in male embryos B) production of estrogens in female embryos C) activation of SRY in male embryos and masculinization of the gonads D) activation of SRY in females and feminization of the gonads