6 (0.5 points) (1) To erase or not to erase? (2) That is the question in many students' minds after they've penciled in one of those small circles in multiple-choice tests, (3) Folk wisdom has long held that when answering questions on such tests-or on any test-you should trust your first instincts. () However, a research instructor has found that students who change answers they're unsure of usually improve their scores, (5) The instructor spent three years compiling and analyzing college students' tests, watching for telltale erasure marks, which would indicate that the student had indeed, revised his or her answer. (6) What the instructor found was that revised answers ware two and athalf times as likely to go from wrong to right as vice versa. (7) This statistic held up evan across such variables as sex, age, and race; the subject matter of the tests studied also proved not to be a factor The sentence that expresses the main idea is