吃透英语课本，提升在校竞争力
adj. 可缩进的；可缩回的；可收回的
When the auto enters the highway system, a retractable arm will drop from the auto and make contact with a rail, which is similar to those powering subway trains electrically.
当汽车进入高速公路系统时，一只可伸缩的手臂将从汽车上落下，与轨道接触，这类似于为地铁列车供电的轨道。
The cat's claws are retractable.
猫的爪子是可伸缩的。
The pen has a retractable tip.
这支笔有一个可伸缩的笔尖。
