<span>c. is the answer .... answer is c. useful </span>
The correct option is B.
Extensive mining started in West Virginia in 1800s. The mining industry was successful in the state due to many reasons. One of the reasons is that, water wheels and burning woods were the major fuels that were used in the industries then, but when coal came around, it become the major fuel that was used by these industries, thus, the demand for it was very high.
“He talks” is a sentence fragment. The word he talks doesn’t show anything. If the sentence was like “He talks like a girl”, it’ll be a complete sentence.