–______ keep water running when you are brushing your teeth or washing your hands, Jack.– OK. I know we must save every drop(滴) of water.A. Why not B. Please C. Don’t
---How long did it _____ you to work out the difficult maths problems? ---I ______ about half an hour on it .
It is very _______ of you to speak in front of all those people .
---Do you often play computer games? ---No, And so do ________ of my classmates, you know we are very busy
I don’t know _____ or not he will come . _______ he comes , I will call you .
The robot needs _______ once a month. And we will check it for you for free.