They ___________ for two hours 
#102329
A
is working
B
worked
C
have been working
D
had worked
推荐题目
 Visitors              not to touch the exhibits.
#99045
A
will request
B
request
C
are requested
D
are requesting
It i s the second time that the poor area_______.
#101272
A
had been visited
B
has been visited
C
was visited
D
is visited
The 2012 London Olympic Games _________ to attract several billion TV viewers around the globe.
#102831
A
is expected
B
will be expected
C
are expected
D
has been expected
Professor Liu has ________ teach psychology since he came to the Central China Normal University.
#104447
A
determination to
B
been determined to
C
been determining to
D
determined to