1. Paper, which is the main writing material today, is invented by the Chinese many years ago.
2. We'd better not throw rubbish into the streets.
3. Americans use lots of slangs so it is difficult for me to understand.
4. Thanks to the progress of science and technology, human life has been/become better and better.
- $Answered_{}$ $by_{}$ $thieukhue_{}$ -
