E-Bay，Amazon and Shopbop are popular websites __________ people can sell goods to each other．
#30510
A
where
B
which
C
when
D
whose
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Children’s brains cannot develop properly _________ they lack protein.
#30134
A
because
B
since
C
when
D
unless
________ the Internet is of great help, I don’t think it’s a good idea to spend too much time on it.
#79667
A
While
B
As
C
Because
D
If