Although the causes of cancer ____we do not yet have any practical way to prevent it.
#105341
A
are being uncovered
B
have been uncovering
C
are uncovering
D
have uncovered
推荐题目
—What's that noise?—Oh,I forgot to tell you.The new machine ________.
#105313
A
was tested
B
will be tested
C
is being tested
D
has been tested
5.---Have you handed in your schoolwork yet?  ---Yes,I have. I guess it ____ now. 
#105345
A
has graded
B
is graded
C
is being graded
D
is grading
New medicines and instruments ______ every day to extend life.
#105334
A
develop
B
are being developed
C
are developing
D
have developed