100 N

a. Phương trình phản ứng hoá học: 3Fe + 2O2 --- Fe3O4

Online learning is becoming more and more popular, but it has several disvantages. Firstly, it is very difficult for students to concentrate as they lack face to face interaction with their teacher and friends. Secondly, looking at the screens constasly is harmful to students' eyes and it causes tiredest , so it is not easy for students too work for too long. Thirdly................... For these reasons i prefer going to school and having offline lessons.