Explanation

Reading the question: the prompt concerns a plan, and we need to find an assumption in the plan. Plans tend to have lots of assumptions, but they can be difficult to think of. We tax polluters, so they pollute less--no assumption jumps out. Without a specific prediction, therefore, we can apply a basic filter to each answer choice: does it have any relevance to whether the plan will work?

Applying the filter: We test the choices for relevance to the plan. In choice (A), reducing pollution is part of our conclusion, but the "number of products" need not be part of it. Choice (B) is not critical to the argument; it doesn't say or claim or require that businesses will like the tax or even survive it. Choice (C) looks relevant. Choice (D) is irrelevant to whether the tax will work. And choice (E) is not required for the plan to work, as we can see by a negation test: say there isn't a way to purify gasses at the point of emission. They could still pollute less, by producing less, or by capturing the air and shipping it into space in sealed containers, or whatever. So choice (E) is out.

Logical proof: We're left with (C), so we apply the negation test. Negating it, we get, "The tax will induce businesses to dispose of their greenhouse gas pollution covertly." That statement, if true, deals a severe blow to the argument. The plan won't achieve its aim if polluters continue to pollute covertly. Choice (C) is indeed critical. The correct answer is (C).