The correct option is
C Testosterone
The region outside the seminiferous tubules in testes is called interstitial spaces. It contains small blood vessels and interstitial cell. These interstitial cells are called Leydig cells. Leydig cells constitute the endocrine tissue of testes. It synthesizes and secretes testicular hormones called androgens. Androgens are a group of male sex hormones, mainly testosterone. Thus, the correct answer is 'Testosterone'.