The most accurate statement regarding why an appeal to logic, emotion, and ethics is more effective than an appeal to just one of those elements is:
"Because certain readers will find one type of appeal more persuasive than others, a piece with a variety of appeals will convince more readers."
This statement acknowledges that different people may respond more favorably to different types of appeals. By including a variety of appeals, a writer can address a broader audience and increase the persuasiveness of their argument, making it more convincing to a wider range of readers.