The Secretary's letter impugns my motives.

该部长的来函质疑我的动机。

The passenger inside the bus impugns motorcycle engine driver in succession.

公交车内乘客纷纷指责摩托车司机。

The Secretary's letter questions my veracity, impugns my motives, and tends to publicly discredit me.

这个秘书拷问我的诚实，指责我的动机，意欲在公众面前败坏我的名誉。