Mr. Smith works as a government official now, but he ________in a middle school for 5 years.
| A．has worked | B．worked | C．had worked |
D．had been working |
Scientists study ____ human brains work to make computers.
| A．when | B．how | C．that | D．whether |
______ in the school campus in spring, we will always noitce a colorful display of flowers.
| A．Walk | B．Having walked | C．Being walking | D．Walking |
It’s great that all the visitors who _______ on the island were saved.
| A．trapped | B．have been trapped | C．had trapped | D．had been trapped |
The operation is _______ success. and the patient is now out of ______ danger.
| A．a; the | B．/ ; / | C．/ ; the | D．a ; / |
At the routine office meeting, the headmaster insisted that the problems _______ paid special attention to.
| A．referred to being | B．referred to be | C．refer to being | D．refer to be |