Define the following terms:
$(1)$ Testosterone
$(2)$ Menstrual flow

(N/A) $(1)$ Testosterone is the primary male sex hormone. It is responsible for the development of secondary sexual characteristics in males.
$(2)$ Menstrual flow refers to the periodic shedding of the endometrial lining of the uterus along with blood vessels and unfertilized ovum,which is discharged through the vagina when fertilization does not occur.