Some people get in touch with each other by mobile phones__________ others keep contact with each other by e-mail.
A. while B. before C .when C. since
The boy burst into tears ________ he saw his mother.
| A．at the moment | B．in a moment | C．for a moment | D．the moment |
Raising environmental awareness was the aim of our art exhibition ____ last week.
| A．to hold | B．held | C．having held | D．being held |
_________ he was, he still went on with his work.
| A．Tired although | B．Tiring as | C．Tired though | D．While tired |
It is ten years since we ________ each other last time．
| A．see | B．have seen | C．saw | D．had seen |
More wild tigers have been seen in the forest around this area, ________ there used to be very few.
| A．when | B．where | C．what | D．which |