There is a big garden in the residential buildings，________actually has become a good place for people to meet and communicate.
| A．where | B．in which | C．that | D．which |
As a result of destroying the forests, a large _____ of desert _____ covered the land.
| A．number, has | B．quantity, has | C．number, have | D．quantity, have |
David helps his mother with her housework every Saturday for about _____.
| A．one and half hours | B．a half and an hour |
| C．an hour and half | D．one and a half hours |
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 |
20．Tell John not to leave the house unless he_____________that the lights .
| A．will make sure，turn off | B．makes sure，are turned off |
| C．will make sure，will turn off | D．makes sure，will be turned off |
19．Mrs．Brown is so_________about her housework that few servants Want to work for her．
| A．skillful | B．neat | C．particular | D．Special |