—Look, the paint is starting to come off
题型：选择题
问题：
—Look, the paint is starting to come off ____ the wall is damp.
—Well, we'd better have the wall repainted some day.
A．when
B．where
C．if
D．once
—Look, the paint is starting to come off ____ the wall is damp.
—Well, we'd better have the wall repainted some day.
A．when
B．where
C．if
D．once