Critical Reasoning

Installing scrubbers in smokestacks and switching to cleaner-burning fuel are the two methods available to
Northern Power for reducing harmful emissions from its plants. Scrubbers will reduce harmful emissions more than cleaner-burning fuels will. Therefore, by installing scrubbers, Northern Power will be doing the most that can be done to reduce harmful emissions from its plants.

Which of the following is an assumption on which the argument depends?
A. Switching to cleaner-burning fuel will not be more expensive than installing scrubbers.

Suppose that 'not' is removed from the above sentence .Can it be an assumption.?