| A．We don’t think it necessary to give students tests every week. |
| B．We don’t have to worry about not having enough to eat now. |
| C．My father has left school for over twenty years. |
| D．He was heard singing a pop song when I passed his room. |
| A．We don’t think it necessary to give students tests every week. |
| B．We don’t have to worry about not having enough to eat now. |
| C．My father has left school for over twenty years. |
| D．He was heard singing a pop song when I passed his room. |