A Levels are generally worked towards over two years. Normally, students take three or four A Level courses in their first year of sixth form, and most taking four cut back to three in their second year. This is because university offers are normally based on three A Level grades, and taking a fourth can have an impact on grades. Unlike other level-3 qualifications, such as the International Baccalaureate, A Levels have no specific subject requirements, so students have the opportunity to combine any subjects they wish to take. However, students normally pick their courses based on the degree they wish to pursue at university: most degrees require specific A Levels for entry.