The window ________ ten minutes ago, and the room is bright now．

A．can be cleaned

B．is cleaned

C．was cleaned

D．will be cleaned

This kind of food ________ cool, clean and dry according to the instruction．

A．should be carried

B．must be put

C．should be placed

D．must be kept

Personal computers ________ in 1976．It has changed the whole world．

A．have been invented

B．are invented

C．were invented

D．invented

－Do you know who designed the CD-ROM Around the world in Eight Hours?

－Yes．It ________ by Nancy Jackson．

A．has designed

B．designed

C．was designed

D．designs

A tsunami(海啸)happened in some south Asian countries ________ December, 2004．

A．at

B．on

C．in

D．by