What is the sentence that expresses the main idea 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. (4) 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 were two-and-a-half times as likely to go from wrong to right as vice-versa. (7) This statistic held up even across such variables as sex, age, and race; the subject matter of the tests studied also proved not to be a factor.