The scientists ________ on the new medicine for two years. They will succeed in no time. 
#38384
A
work
B
are working
C
have worked
D
will work
推荐题目
Hurry up! The play _______ for half an hour.
#40061
A
has been on
B
has began
C
has begun
D
had begun
Our teacher told us that light _____ much faster than sound.
#41507
A
traveled
B
travels
C
is traveling
D
was traveling
What ________ you ________ at this time yesterday?
#37876
A
did, do
B
have, done
C
were, doing
D
are, doing