只要你提前三个月预订,飞往悉尼的票价就会减半。
The air ticket to Sydney will be half price _______________________ it three months earlier.
as long as/ if you book
若实数x、y满足xy>0,则xx+y+2yx+2y的最大值为( )
浸在液体中的物体如果受到浮力作用,那么施力物体是( )