Don’t be in a hurry. We are supposed ____________ this problem step by step.
| A．solving | B．to solving | C．to solve | D．solve |
30. He was told that it would be at least three more months ______ he could recover and return to work.
| A．when | B．before | C．since | D．that |
29. The field research will take Joan and Paul about five months; it will be a long time ______ we meet them again.
| A．after | B．before | C．since | D．when |
28.“When did he leave the classroom?” “He left _______ you turned back to write on the blackboard.”
| A．the time | B．the moment | C．until | D．since |
27. “Shall Mary come and play computer games?”
“No, _______ she has finished her homework.”
| A．when | B．since | C．unless | D．as soon as |
26. The visitor asked to have his picture taken _______ stood the famous tower.
| A．that | B．at which | C．when | D．where |