Most people in CAS don't officially declare their major until sophomore year. I did it at the end of freshman year so I could get an adviser in my major field of study. Cornell puts that on the application just to get an idea of what its incoming class plans on studying and they will make an effort to assign you an adviser within your major, which is more important in some majors than others. I actually got an adviser in the field I applied for, but then I switched which major I wanted. But definitely don't worry about declaring your major. The advantage to CAS is that it offers by far the most diversified education of any college at Cornell so you may change your idea of exactly what you want to major in, especially in something as broad as English/history.