The correct answers are the following:
1. Euphemism: "stretching the truth"
2. Oxymoron: "bittersweet"
3. Euphemism: "was put to sleep"
4. Oxymoron: "living dead"
Euphemism is a gentle or indirect word or phrase which substitutes another that is too harsh or rude. It usually refers to unpleasant or humiliating situations.
Oxymoron is a figure of speech in which two opposite terms are together.