a treacherous ally的用法和样例：
- A treacherous fellow is the Shark.
- I know of you Red Wizards. You are a treacherous lot.
- It seems that deciding whether any memory is to be finally assessed as reliable or the treacherous ally of invention will largely remain a challenge for judges and juries.
- A treacherous coward who betrayed his friends to save his own skin.
- This was a treacherous act of betrayal by the Irish.