The underlined part of the given sentence 'if they rate the watt-hour higher, the longer' can be replaced with a better phrase from the given options. Option A) is the same phrase and so is the incorrect answer. Option B) is incorrect as it doesn't fit into the tone of the sentence. Option C) is the correct form of writing the phrase better and so is the correct answer. Options D) and E) are both incorrect as they don't fit into the tone of the sentence.