1.-----There's someone knocking at the door.Who could ____be

1.-----There's someone knocking at the door.Who could ____be?
-----I have no idea.
A.he B.it C.she D.that
2.At one time we had about eighty people here who did nothing but ____into various family history.
A.researched B.research C.researching D.to research
3.Your hair needs____.You'd better have it done tomorrow.
A.cut B.cutting C.to cut D.being cut
4.-------How____will you be able to come back from you travel?
-------In a couple of weeks,perhaps.
A.fast B.long C.often D.soon