She ____ on her homework in her study now .
| A．must work | B．can work | C．must have worked | D．must be working |
The Christmas gifts need to be ready next Friday.
| A．by | B．of | C．in | D．at |
For the engine to work, the green button be in the “on” position.
| A．can | B．would | C．must | D．might |
Kids are not allowed to leave kindergartens their parents come to pick them up.
| A．since | B．unless | C．although | D．because |
I have to walk upstairs. The lift down.
| A．was breaking | B．broke | C．will break | D．has broken |
Joseph off at the airport, Sally finished her work earlier.
| A．Having seen | B．Seen | C．To see | D．To be seen |