HEL Some factories that burn coal produce smoke with harmful chemicals, such as sulfur. Scrubbers are devices that are attached to the smokestacks to reduce the amount of sulfur put into the atmosphere. To evaluate the effectiveness of these devices, what data would need to be collected? A. The percentage of sulfur contained, on average, in a certain amount of coal

B. The amount of coal a factory burns each year, and how much sulfur it emits

C. The increase, over time, in the use of scrubbers by factories that burn coal

D. The amount of sulfur emitted by a smokestack before and after the scrubber is attached