除非...才...
chú fēi ... cái ...
Only if...，will...; Unless...，...
除非明天下大雪，会议才会取消。
chú fēi míng tiān xià dà xuě ，huì yì cái huì qǔ xiāo .
Only if it snows heavily tomorrow will meeting be cancelled.; Unless it snows heavily tomorrow，the meeting will not be cancelled.
