Let's analyze the pronunciation of the underlined parts in the given words:

**3.**
- A. **celebrate**: /ˈsɛl.ɪ.breɪt/
- B. **religious**: /rɪˈlɪdʒ.əs/
- C. **salmon**: /ˈsæm.ən/ (the "l" is silent)
- D. **facilities**: /fəˈsɪl.ɪ.tiz/

**Explanation**:
- In this case, the word **C. salmon** differs because the "l" is silent, whereas the other words pronounce all their letters clearly.

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**4.**
- A. **western**: /ˈwɛs.tərn/
- B. **wonder**: /ˈwʌn.dər/
- C. **highway**: /ˈhaɪ.weɪ/
- D. **wreckage**: /ˈrɛk.ɪdʒ/

**Explanation**:
- In this case, **C. highway** differs in vowel sound because it contains the diphthong /aɪ/, while the other words involve shorter vowel sounds.

So the answers are:
- **3. C. salmon**
- **4. C. highway**