To make us healthier, the teachers often see us ______ on the playground. 

-- The math problem _________ is not difficult. --- But after several tries , I have to give up _________ on it .

I think the lives of children in poor areas _____ greatly by this project. 

I’m very lonely .I’d like to find someone         

—It’s too hot . Would you mind my ____ the window?—_______ . Do as you like, please!