Here are the answers to the word stress exercise:

1. A. **pollution** (main stress on the second syllable) - others are first syllable stressed.
2. A. **destroy** (main stress on the second syllable) - others are first syllable stressed.
3. A. **diverse** (could be first or second syllable stressed, but often the second) - others are first syllable stressed.
4. A. **become** (second syllable stressed) - others are first syllable stressed.
5. A. **voucher** (first syllable stressed) - others have varying stress patterns, but B. **shuttle** can also be first syllable stressed while C. **online** and D. **usual** have different patterns.

Thus, the main outlier for most is **A in each group**, particularly for the first four questions.