FILL IN THE BLANKS OF THE FOLLOWING LETTER WITH GIVEN SENTENCES IN THE BOX. __1___,mobile phones are being more and more widely used. It's small in size, ___2__, offering fast and convenient service for communication. It's of multi-function. __3___. In recent years,__4___Quite a few use them at school to keep in touch with their families and friends instead of writing letters, which, of course brings convenience to them. But I don't think it's good to do so. __5___, student users often waste a lot of time chatting over the phone in their spare time, some even use them to cheat in exams. In addition, mobile phone bill is also a heavy burden on students' families.