Generally, high school years usually have two semesters, starting in September and February. In some rural areas, the operation may be subject to agricultural cycles. The number of lessons offered by a school every week is very subjective and largely depends on the school's resources. In addition to normal lessons, periods for private study and extracurricular activity are provided as well. The academic curriculum consists of Chinese, Mathematics, English, Physics, Chemistry, Biology, Geography, History, Ideology & Political Science, Music, Fine Arts, PE, Technology, Computing, etc. Some schools may also offer vocational subjects. Generally speaking, Chinese, Mathematics, and English are considered as three main subjects as they will definitely be examined in Gaokao. In most provinces, students also need to be examined in either natural sciences, which incorporate Physics, Chemistry and Biology, or social sciences, which incorporate Geography, History, and Ideology & Political Science.