________ students in the classroom ______ twenty. The others are in the library.
| A．The number of ; is | B．A number of; are |
| C．The number of; are | D．A number of ; is |
— Do you believe that paper is made _______ wood?
—Yes, I do. And you can see that books are made________ paper.
| A．from; from | B．from; of |
| C．of; from | D．of; of |
______ is said that our math teacher often does volunteer work on weekends.
| A．One | B．This | C．It | D．That |
I took the wrong train _______. I didn’t even know it until half an hour later .
| A．by mistakes | B．by mistake |
| C．with mistake | D．with mistakes |
The mobile phone has influenced people’s life a lot since it ________.
| A．invents | B．invented |
| C．is invented | D．was invented |