Which of the following structures does not exist as a pair? Select one: a. The kidney. b. The sphincter muscle. c. The ureter. d. The urethra.

Answer:The sphincter muscle is not a pair

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.