7.Although the causes of cancer ____， we do not yet have any practical way to prevent it.
#105343
A
are being uncovered
B
have been uncovering
C
are uncovering
D
have uncovered
推荐题目
What shall we use for power when all the oil in the world has ?
#105323
A
given out
B
put out
C
held up
D
used up
Since 1 won the big prize，my telephone hasn’t stopped ringing. People____to ask how I am going to spend the money.
#105338
A
phone
B
will phone
C
were phoning
D
are phoning
一Ready to give up guessing，Sandy?一No，no，hold on! I think I______ at the answer now．
#105346
A
arrive
B
am arriving
C
have arrived
D
will arrive
—I'm not finished with my dinner yet.—But our friends ________ for us.(2010·北京)
#105317
A
will wait
B
wait
C
have waited
D
are waiting
—Believe it or not! I should get my lost wallet back after I left it in the taxi this morning.—Couldn’t agree more! You know, someone _______ it. There are still good persons in Chongqing.
#105322
A
can have taken
B
might have taken
C
should have taken
D
must have taken