The problem will appear ______ a different welfare system will be careated.

The problem will appear ______ a different welfare system will be careated.
A.unless
B.whether
C.until
D.if
Where did you get such a beautiful skirt?
It was at the department store ______ we uded to shop.
A.that
B.there
C.where
D.which
A survey was conducted in Shanghai _______ interviewees were asked if they wanted to be a factory worker.
A.when
B.which
C.that
D.where