back and forth 来回地，反复来回，向后再向前

【例句】
Through the open window I saw my comrades already in their places, and Monsieur Hamel walking back and forth with the terrible iron ruler under his arm.
透过敞开的窗户，我看见同学们已经整整齐齐地坐在他们的座上，阿麦尔先生腋下夹着那把可怕的铁戒尺，来回地踱着步子。

She rocks back and forth on her chair like a mischievous child.
她像个顽皮的孩子似的，坐在椅子上来回摇晃。