The world is now using 10 times as much wanter as it did 100 years ago.Scientists say that by 2020watei shortage will be a serious world problem.Clean water is precious and it's t_____for all of us to learn to save it!
问题描述：
The world is now using 10 times as much wanter as it did 100 years ago.Scientists say that by 2020watei shortage will be a serious world problem.Clean water is precious and it's t_____
for all of us to learn to save it!
答