They ________ often _______to be careful before _______the road.
________ students in the classroom ______ twenty. The others are in the library.
— Do you believe that paper is made _______ wood?—Yes, I do. And you can see that books are made________ paper.
______ is said that our math teacher often does volunteer work on weekends.
I took the wrong train _______. I didn’t even know it until half an hour later .
The mobile phone has influenced people’s life a lot since it ________.