The man in the office ____be Mr. Black because he phoned me from London just now.

About ______ of the books in our school library are written in Chinese.

The environment is becoming worse and worse. I think we should do something to ____ people ____ cutting the trees in order to protect the earth.

Where is Mike? —He’s _______ the pool.

A new to teaching languages is being used here, and it has turned out to be very helpful to the students.