No one really knows exactly when the first people arrived in we now know as California.
| A．that | B．which | C．what | D．where |
My parents have promised to come to see me before I _________ for Africa.
| A．have left | B．leave | C．left | D．will leave |
Charles Babbage is generally considered to _______ the first computer.
| A．to invent | B．inventing | C．to have invented | D．having invented |
----I have got a headache.
---- No wonder. You ________ in front of that computer too long.
| A．work | B．are working | C．worked | D．have been working |
The police ________ the lost child and tried to find his parents.
| A．took up | B．took in | C．took over | D．took after |
It’s very hard for Mary to work here, for ______ she does can’t satisfy her boss.
| A．what | B．whatever | C．which | D．whichever |