What structure is described as a sac behind the pubic symphysis that collects and stores urine?

The correct answer is the urinary bladder, which is a muscular sac located behind the pubic symphysis. Its primary function is to collect and store urine produced by the kidneys until it is ready to be excreted from the body. The bladder is able to expand and contract as it fills and empties, and it connects to the urethra, which is the duct through which urine is discharged.

In this context, the kidneys are responsible for filtering blood and producing urine, but they do not collect or store urine; instead, they release it into the ureters, which then transport urine to the bladder. The urethra is simply the passageway for urine to exit the body and does not function as a storage structure. The renal tubule is part of the nephron in the kidney where urine formation occurs, but it is not involved in the collection or storage of urine. Hence, the urinary bladder is uniquely suited to the task described in the question, making it the correct answer.