In order to determine the meaning of the word "daunting" in this sentence, we can look for context clues. The sentence provides information that William is afraid to begin the task of writing his research essay and that he has never written more than five pages before. From this information, we can infer that the task of writing the research essay is overwhelming or intimidating for William. Therefore, the correct answer is intimidating.
In the sentence, the word daunting means intimidating.