Due to COVID-19, online course has become     1     hot topic. Some people are in favor of it. They think students can follow teachers to keep     2    (learn). With the videos saved in the computer, students can review what they have learned at any time. But other people are worried that students may play games while studying and waste their time. Students might become addicted to phones,     3     has a bad impact on their study. What’s worse, too much screen time does great harm to students’ eyes.