当他成功后，便不再与他以前的朋友来往。

He ___turned ___his ___back ___on his old friends when he became successful.

她断绝了与家人的联系，搬到了国外。

She ___turned ___her ___back ___on her family and moved abroad.

在他们最需要帮助的时候，他拒绝伸出援手。

When they needed help the most, he ___turned ___his ___back ___on them.