Sắp xếp lại các câu sau

----- Nội dung dịch tự động từ ảnh -----
30. wasting water / will be / in a few decades/ a shortage of fresh water/ there / if we go on.
21
29. students / by keeping sheets / for drafting / can reuse paper / with single printed page.
28. no cracks /Why don't you / in the pipes / there are / to make sure / get a plumber /?
Why don't you
....
.....
- Students
.....
If we go on
w..... ..
31. by/ can be reduced / energy-saving bulbs / the monthly amount of electricity
we use / with / replacing ordinary 100-watt light bulbs.
The monthly amount of electricity we use .....