I would choose A. Samantha is testing the actual question "how many LIBRARY books are checked out by 7th graders at SAME time". She is still getting a result to the question, but an inaccurate reading as we do not know if ALL 7th graders are present in library and she is only doing a portion of 7th graders checking out books. However, Luis is going to cafe and some may never have gone to library or dislike reading tangible material. Basically both are bad surveyors, but Luis is definlately performing a more random approach.