Here are the answers for each question:

1. **A (flat)** - differs because the vowel sound is /æ/ while the others have /e/ or /ɪ/.
2. **C (nation)** - differs as the vowel sound is /eɪ/ while the others have /ɛ/ or /ə/.
3. **C (juice)** - differs because the vowel sound is /uː/ while the others have /aɪ/ or /ɪ/.
4. **D (highland)** - differs in having the vowel sound /aɪ/ while others have /ɪ/ or /e/.
5. **A (about)** - differs because the vowel sound is /aʊ/ while the others contain /ɪ/ or /a/.
6. **D (alive)** - differs because it has the /aɪ/ sound while the others vary in vowel sounds.
7. **C (through)** - differs in having /uː/ sound, while others have a different vowel sound.
8. **C (health)** - differs in vowel sound /ɛː/ compared to other options.
9. **A (washes)** - differs as it has the /ʃ/ sound, whereas other words have different sounds.
10. **A (happiness)** - differs because it uses the /æ/ sound compared to the other options.

Feel free to confirm for any specific word or explanation!