(1)∵∠1=∠ABC(已知),
∴AD∥BC,(同位角相等两直线平行)
(2)∵∠3=∠5(已知),
∴AB∥CD,(内错角相等两直线平行)
(3)∵∠ABC+∠BCD=180°(已知),
∴AB∥CD(同旁内角互补两直线平行)