An imported wool fiber available in black or brown with a matte finish that is used in hair extension is:

The correct answer is yak fiber. Yak fiber, particularly when imported, is available in natural colors such as black or brown and typically has a matte finish. This type of fiber is prized in hair extensions due to its unique qualities, including warmth and softness, making it suitable for a natural look and feel in hair applications.

Furthermore, yak fibers possess a level of durability that is beneficial for hair extensions, allowing them to withstand styling and daily wear. The matte finish of yak fiber is especially desirable in the realm of hair extensions, as it provides a more natural appearance compared to shinier synthetic or processed fibers. In contrast, the other options listed lack the specific characteristics of yak fiber, such as the color range and matte finish desirable for hair extensions.