Final answer:
The male reproductive duct that is six meters long when uncoiled but fits into a 3.5-cm area when coiled is the ductus epididymis.
Step-by-step explanation:
The male reproductive duct that is approximately six meters long but is tightly coiled into a 3.5-cm distance is the ductus epididymis (B). This coiled tube is attached to the testis where newly formed sperm continue to mature. While the epididymis does not occupy much space due to its coiled state, it would measure around 6 meters if it were to be uncoiled. Sperm take on average 12 days to transit through the epididymis, developing the capacity to move independently which will later aid them in traveling towards the unfertilized egg in the female reproductive tract. Mature sperm are eventually stored in the tail of the epididymis until ejaculation.