Final answer:
The sentence should be changed to "The most powerful of all these chemicals, DDT was banned in the United States."
Step-by-step explanation:
The correct way to change the sentence is option B. The sentence should be written as "The most powerful of all these chemicals, DDT was banned in the United States." This change ensures that the superlative form of the adjective 'powerful' is used to compare DDT with the other chemicals mentioned. The word 'powerfullest' in option C is not a correct word and should be avoided. Option A is incorrect because it uses 'powerfully' which is an adverb, not an adjective.
Learn more about sentence correction