Answer:The sphincter muscle is not a pair
Explanation:
Answer: The urethra
Explanation: All except the urethra in the give options do not exist as a pair in the body system. The urethra is defined anatomically as the tube through which urine exits the body and, in penises, is the tube through which semen is ejaculated. It is the tube that connects the urinary bladder to the urethral opening on the external genitals in both males and females.
