The correct option is D Isthmus
Females have two fallopian tubes that extend laterally from the uterus. Each fallopian tube consists of three regions: infundibulum, ampulla and isthmus.
Uterus also known as the womb is a single structure and is a pear-shaped muscular organ in females.
Vagina is a fibromuscular tube that receives the sperms. It also forms the birth canal along with cervical canal.
Prostate gland is a structure located just beneath the urinary bladder in males and is a male accessory gland. The secretion of the prostate enhances the motility of the sperm. Prostate is an unpaired gland.
Hence, isthmus is a paired structure in the options given below.