The correct answer is: Mark Twain is one of the best-known authors in American history.
One of the most important and most difficult steps in the research process is selcting the topic. As the first step, if it's not done properly the entire process might be compromised. In this case the research requires too much information to be accomplished, as it needs to prove the reasons of his superiority amongst the other authors. A comparison between their styles of writting, the context they wrote and the repercussion they had done is necesary to fulfill this objective. It is important to emphasize the fact that the statement is refering to all American history so there are too many authors ans styles to compare making it a very profound research.
The other options have a more delimited objective which need specific information to be completed and therefore less time is needed.
