The correct answer is b. LH.
Luteinizing hormone (LH) is a pituitary hormone with the influence on both, male and female reproductive system, regulated by gonadotropin-releasing hormone (GnRH). In males, LH acts upon the interstitial cells (or Leydig cells) of the testis, which produce testosterone. LH regulates the expression of the enzyme that is used to convert the precursor of the testosterone to testosterone.
