______ to improve our environment

Encourage your children to try new things, but try not to__________them too hard.

There will be ________water and ________trees in 100 years, how can we live

You look so tired, Sue.— I _____ slept last night. I feel very terrible now.

I listened to Professor Chen-Ning Franklin Yang’s lecture about his study and physics, but I failed to get its key ______ .