For example, improved scrubber performance and the ability of some firms to switch to lower sulfur fuels under the Acid Rain Program were reasons the cost of that program were less than projected.
The switch to lower sulfur fuels was not a requirement for all firms.
mnli hypothesis: The switch to lower sulfur fuels was not a requirement for all firms. premise: For example, improved scrubber performance and the ability of some firms to switch to lower sulfur fuels under the Acid Rain Program were reasons the cost of that program were less than projected.