Answer:
A. James Neilson’s furnace invention provided a new heat source.
Explanation:
In the passage it states... "Then, a Scotsman named James Neilson invented the hot blast furnace... Once the hot blast technique was perfected, anthracite was in demand all over the world." This proves why it was in high demand. Everyone wanted to use it! It could not be B. Pennsylvania’s mining industry boomed, causing an increase in supply. Because that would not be a reason for the demand to go up. C. Anthracite provided a cheaper, widely available, and more effective source of heat, is true, but that still is not a reason for the demand to increase all over the world. D. Because anthracite could only be found in Pennsylvania, other countries were eager to import it is tricky. It is true, but there is no evidence stating this in the passage.
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