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Given a context passage, generate a question from the passage such that its answer is shortest continous span from the passage.

The male reproductive organs include the penis, testes, and epididymis ( Figure 1.1). The figure also shows other parts of the male reproductive system. The penis is a cylinder-shaped organ. It contains the urethra. The urethra is a tube that carries urine out of the body. The urethra also carries sperm out of the body. This drawing shows the organs of the male reproductive system. It shows the organs from the side. Find each organ in the drawing as you read about it in the text. The two testes (singular, testis) are egg-shaped organs. They produce sperm and secrete testosterone. The testes are found inside of the scrotum. The scrotum is a sac that hangs down outside the body. The scrotum also contains the epididymis. The testes, being in the scrotum outside the body, allow the temperature of the sperm to be maintained at a few degrees lower than body temperature. This is necessary for the stability of these reproductive cells. The epididymis is a tube that is about six meters (20 feet) long in adults. It is tightly coiled, so it fits inside the scrotum. It rests on top of the testes. The epididymis is where sperm grow larger and mature. The epididymis also stores sperm until they leave the body. Other parts of the male reproductive system include the vas deferens and the prostate gland. Both of these structures are pictured below ( Figure 1.1). The vas deferens is a tube that carries sperm from the epididymis to the urethra. The prostate gland secretes a fluid that mixes with sperm to help form semen. The prostate gland is located beneath the bladder. Semen is a "milky" liquid that carries sperm through the urethra and out of the body. In addition to sperm cells, semen contains sugars (fructose) which provide energy to the sperm cells, and enzymes and other substances which help the sperm survive.
Output:
what is the organ where sperm cells mature?