2. Every course in Senior One begins with a compulsory course. If you want to preview in advance, buy the required auxiliary materials of 1 and use them in the first semester immediately. I didn't choose a subject in senior one. All subjects need to be studied.
Elective, the school will arrange courses for you to choose whatever you learn. 1-11-21-3 means to select a book to enter these three volumes, and 3-5 means to select the fifth of the three volumes. When you study, you will understand, and you will not be so confused. High school textbooks are like this.