Science has given clear evidence ______ smoking can lead to many diseases.
#31076
A
what
B
which
C
that
D
where
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Sometimes, ___ we show our gratitude for a person is reflected in the kind of food we serve him or her．
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whether
B
when
C
why
D
how
Studying in groups is necessary_____ you want to do well in school.
#30854
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if
B
until
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D
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The government has taken some measures to solve the shortage of electricity, but it may be some time ____________ the situation improves.
#31321
A
since
B
when
C
unless
D
before