短语词组短语Fork Backrest 双叉靠背backrest bushing 靠背轴套adjustable backrest 可调式靠背backrest block 后立柱移动块backrest knob 靠背调整旋钮Foldable Backrest 靠背可High Backrest 高靠背Backrest locking 靠背锁Backrest design 腰垫设计 返回 backrest