Although the causes of cancer_____, we do not yet have any practical way to prevent it.
#104936
A
are being uncovered
B
have been uncovering
C
are uncovering
D
have uncovered
推荐题目
The committee __ over the problem among themselves for two hours.
#100019
A
has argued
B
has been arguing
C
have argued
D
have been arguing
Some modern teaching equipment as well as hundreds of computers _______ to ten Hope Schools in South China．
#102408
A
were sent
B
was sent
C
have sent
D
had been sent
The little boy is dirty from head to foot because he______in the mud all morning.
#104172
A
has played
B
is playing
C
has been playing
D
was playing
— You look tired.— Yes. I ___ non-stop until 8 o’clock this morning.
#102703
A
had worked
B
work
C
have worked
D
was working
The twins, Who their homework, were allowed to play badminton on the playground.
#99095
A
will finish
B
finish
C
have finished
D
had finished