AIDS is said________the biggest challenge to both men and women in that area over the past few years.
| A．that it is | B．to be |
| C．that it has been | D．to have been |
To enjoy the scenery, Irene would rather spend long hours on the train _____ travel by air.
| A．as | B．than |
| C．to | D．while |
Professor Smith, along with his assistants, _____on the Project day and night to meet the deadline.
| A．work | B．working |
| C．is working | D．are working |
He met his previous teacher ________ at abroad.
| A．by any chance | B．by the chance |
| C．by chance | D．by a chance |
Tom, ______ yourself .Did you forget the school rules?
| A．behave | B．believe |
| C．perform | D．conduct |
He is the only one of the students who ______a winner of a scholarship for three years.
| A．is | B．are |
| C．have been | D．has been |