题干
如图，a∥b，点P在直线a上，点A，B，C都在直线b上，PA⊥AC，且PA=2cm，PB=3cm，PC=4cm，则直线a，b间的距离为____ cm．
答案(点此获取答案解析）
2
，a 
，a 
，a 
，a 
and a 
in the room.There is a 
on the wall. There are some 
on the desk.There is a new 
on the desk，too. I like my room.