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 are you putting your shoes on again for?—Because I________you home, that’s all!
#105304
A
drive
B
am driving
C
have driven
D
drove
Hurry up，kids！The school bus ________for us！ (2013·四川，3)
#105306
A
waits
B
was waiting
C
waited
D
is waiting
--- Would you care for a cup of coffee? --- I ________ one. Thank you just the same.
#105330
A
had
B
have had
C
would have
D
will have
Today many physical bookstores ________ down with financial difficulties, inflexible management strategies and competitive pressure from online bookstores.
#105310
A
had closed
B
having closed
C
being closed
D
are closing
一Have you handed in your schoolwork yet?一Yes,I have.I guess it _____ now.
#105339
A
has graded
B
is graded
C
is being graded
D
is grading