From the options you added in the comments box, the one that does not contain an euphemism is the first one: 90% of the class failed.
The correct answer is A).
An euphemism is a mild or indirect expression or word that substitutes for one considered to be too harsh or blunt when referring to something unpleasant or embarrassing.
In this case, the purpose of the teacher was to tell the students the bad news about the exam's results trying not to hurt them.
