They ________have arrived at lunchtime but their flight was delayed.
| A．will | B．can |
| C．must | D．should |
__________ in thought, he almost ran into the car in front of him.
| A．Losing |
| B．Having lost |
| C．Lost |
| D．To lose |
__________ in 1636, Harvard is one of the most famous universities in the United States.
| A．Being founded |
| B．It was founded |
| C．Founded |
| D．Founding |
When __________, the museum will be open to the public next year.
| A．completed |
| B．completing |
| C．being completed |
| D．to be completed |
The research is so designed that once __________ nothing can be done to change it.
| A．begins |
| B．having begun |
| C．beginning |
| D．begun |
__________ more attention, the trees could have grown better.
| A．Given |
| B．To give |
| C．Giving |
| D．Having given |