at a time 依次;每次

【例句】
Prepare medications for one client at a time.
按病人依次准备药物。

Another great relaxationtechnique is to tense up and then relax each musclein your body, one at a time, starting from your toes up to your head.
另一个放松技巧是让你身体的每块肌肉依次先收缩后放松。从脚趾开始往上，至头部结束。