There are many extracurricular exams. I have participated in the national chemistry competition for senior high school students, and I can hardly test the contents in books. Instead, I want you to use books to solve extracurricular content, chemical engineering, real life and other topics, so that you can write principles and chemistry or ionic equation, have a plenty of calculation problems, and learn which part. In addition, I basically read the content about this in the high school textbooks. Don't take part in proposals with poor foundation. It will be difficult to write questions, which will help the college entrance examination and stimulate your enthusiasm for this subject. If you have more time and a good foundation in all subjects, you can participate more. If you have a good foundation in only one subject, I suggest you take part in the competition in only one subject, and you can't study only one subject without studying other subjects, so you will suffer unless you can make it to the national finals.