To their surprise, they found the lecture given by the famous professor easy ______.
| A．to be understood | B．to understand |
| C．understanding | D．understood |
When you read the book, you’d better make a mark _____ you have any questions.
| A．at which | B．at where |
| C．the place where | D．where |
You should let your children play ______ you can see them.
| A．where | B．when |
| C．in which | D．that |
Now he works in the factory ______ his father used to work.
| A．where | B．when |
| C．in which | D．that |
The visitor asked to have his picture taken _______ stood the famous tower.
| A．that | B．at which |
| C．when | D．where |
They kept trying _____ they must have known it was hopeless.
| A．if | B．because |
| C．when | D．where |