in both directions alternately; to and fro
來來回回
he paced backwards and forwards nervously.
他緊張地來回踱步。
(informal)make every effort to achieve something, especially to be fair or helpful
(非正式)竭盡全力（尤指為實(shí)現(xiàn)公平或給予幫助）
we have bent over backwards to ensure a fair trial for the defendants.
我們竭盡全力保證對被告公平審判。
be entirely familiar with something
了如指掌