Perhaps the day will come ____ people will be able to breathe clean air in cities．
#32785
A
when
B
while
C
as
D
since
推荐题目
The field research will take Joan and Paul about five months; it will be a long time ____ we meet them again.
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A
after
B
before
C
since
D
when
_A container weighs more after air is put in, ____proves that air has weight.
#80057
A
as
B
it
C
that
D
which
Energy, passion and a burning desire are, you see, ________ true learning takes.
#30345
A
that
B
what
C
how
D
which