Here are the words with a different pronunciation in the underlined parts:

1. **C. drops** (the 'o' is pronounced differently than in 'popular' and 'control')
2. **C. volunteer** (the 'eer' has a different pronunciation compared to 'opportunity' and 'originate')
3. **C. cooked** (the 'oo' has a different sound than in 'donated' and 'passed')
4. **C. prefer** (the 'er' sounds different than in 'midterm' and 'pepper')

So the answers are:
1. C
2. C
3. C
4. C