in both directions alternately; to and fro
来来回回
he paced backwards and forwards nervously.
他紧张地来回踱步。
(informal)make every effort to achieve something, especially to be fair or helpful
(非正式)竭尽全力（尤指为实现公平或给予帮助）
we have bent over backwards to ensure a fair trial for the defendants.
我们竭尽全力保证对被告公平审判。
be entirely familiar with something
了如指掌