—Twice a year.

根据对话内容和所给汉语提示，在空白处填入单词的正确形式。每空限填一词。
Dear students,
      As we all know, good health is important for success in exams, so I’m   ____   (写) to give you all some ways which are   ____   (有帮助的) to you
       First of all, it is necessary that you sleep well    ____   (在……期间) the exam period in order that you can have  ____   (足够的) energy. Second, a healthy, balanced  ____   (饮食) is important to your success. In order to eat healthily, try to avoid eating food high in fat. It’s   ____  (更好) for you to eat a lot of vegetables and fresh fruit which are  ____  (充满) of vitamins. Besides, don’t forget to take exercise no matter how busy you are. It can help you build a strong ____    (身体) as well as making you relaxed.
 ____  (另一个) way I will share with you is this: studying with other people will help you discuss and form your own ideas. Plus, you won’t feel  ____  (孤单的)!
   Best wishes and stay healthy.
                                                                                                                                                 Yours,
                                                                                                                                                 Li Hua