他们一直在背后讨论这笔交易吗？

Have they been discussing the deal ___behind ___his ___back?

一些同事在新经理背后发表了批评性言论。

Some colleagues made critical comments ___behind ___their ___new manager's ___back.

她瞒着伴侣秘密申请了那份工作。

She secretly applied for the job ___behind ___her ___partner's ___back.