alternates

英[ˈɔːltə(r)neɪts]

v. 交替( alternate的第三人称单数 ); （使）交替, （使）轮换

n someone who takes the place of another person\nv go back and forth; swing back and forth between two states or conditions\nv exchange people temporarily to fulfill certain jobs and functions\nv be an understudy or alternate for a role\nv reverse (a direction, attitude, or course of action)\nv do something in turns