From my understanding, Euphemism is when you use a mild or an indirect word. So if you are saying something serious, and someone uses a Euphemism (if that's the proper way of using the word "Euphemism"), it could ruin the conversation and it would make you feel like a terrible person. So there for, D is the correct answer
D. When it minimizes the seriousness of something
(Anyone can correct me if I'm wrong, thanks!)
Have a great day!