Here are the words with their main stresses indicated:

1. A. **pollution** (stress on second syllable)
B. **protection** (stress on second syllable)
C. **interest** (stress on first syllable)
D. **announcement** (stress on second syllable)

**Answer: C. interest**

2. A. **destroy** (stress on second syllable)
B. **contain** (stress on second syllable)
C. **detail** (stress on second syllable)
D. **reduce** (stress on second syllable)

**Answer: None are different; all stress the second syllable.**

3. A. **diverse** (stress on second syllable)
B. **unsafe** (stress on second syllable)
C. **marine** (stress on second syllable)
D. **harmful** (stress on first syllable)

**Answer: D. harmful**

4. A. **become** (stress on second syllable)
B. **special** (stress on first syllable)
C. **open** (stress on first syllable)
D. **online** (stress on second syllable)

**Answer: B. special and C. open have stress on the first syllable, others have stress on the second syllable.**

5. A. **voucher** (stress on first syllable)
B. **shuttle** (stress on first syllable)
C. **online** (stress on second syllable)
D. **usual** (stress on first syllable)

**Answer: C. online**

Overall answers for Main Stress Difference:
1. C (interest)
2. None
3. D (harmful)
4. B or C (depends on whether you accept both)
5. C (online)