Final answer:
The best description for the ureters is that they are retroperitoneal structures that actively propel urine from the kidneys to the urinary bladder using smooth muscle induced peristalsis. They are not 'urethrae' nor do they contain skeletal muscle or float freely within the abdominal cavity.
Step-by-step explanation:
The ureters function as the ducts that carry urine from the kidneys to the urinary bladder. They are characterized as being retroperitoneal, which means they are located behind the peritoneal cavity of the abdomen. The ureters are around 30 cm long, have a lumen lined with transitional epithelium, which is capable of expanding. Their walls contain a layer of smooth muscle fibers arranged in longitudinal and circular layers, allowing them to peristaltically propel urine towards the bladder without relying on gravity. The ureters passively do not drain into the bladder but are actively propelled by these muscle contractions. The description of the ureters having specialized subdivisions called urethrae is incorrect, as 'urethrae' refers to the singular 'urethra,' the tube leading from the bladder to discharge urine outside the body. Therefore, the option that best represents the ureters is c. Retroperitoneal.