There are several research centers in China ________ a certain disease called Bird Flu is being studied. 
#73321
A
which
B
where
C
when
D
what
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They promised to develop a software package by the end of this year, ________ they might have.
#67763
A
however difficult
B
how difficult
C
whatever difficulty
D
what difficulty
No matter ______ the CRH accident in Wenzhou, it had and will have much warning significance.
#67709
A
how the investigators said caused
B
what the investigators said caused
C
why the investigators said caused
D
the investigators said how caused