---- Where _______ my books?---- Sorry, I don’t know.

Our school had about 20 notebook computers but only one-forth_____used regularly. Now we have 50 working all day long.

He’s got himself into a dangerous situation _____ he is likely to lose control over the plane. 

All we need     a small piece of land where we can plant various kinds of fruit trees throughout the growing seasons of the year.

Three months ________ since we met last time.