Here are the words with different stress patterns from the others in each listed group:

1. **B. volunteer** - The stress is on the last syllable, unlike the others.
2. **A. mention** - Compared to the others, it has a different stress pattern (stress on the first syllable vs. others).
3. **A. become** - Has the stress on the second syllable, different from others.
4. **A. popular** - Stress is on the first syllable, while others have different patterns.
5. **A. activity** - The stress is on the second syllable, differing from the others.
6. **B. happy** - Has a different stress pattern compared to the other options.
7. **C. garden** - The stress pattern is different from the others.

You can examine each group to determine which word stands out based on its stress pattern.