Here are the mistakes for each underlined part of the sentences:

1. **A**: "Everyone thinks" → should be "Everyone thinks" (correct)
- No mistake.

2. **B**: "that Josh starts" → should be "that Josh started" (past tense)

3. **C**: "I think" → should be "If I didn't think" (conditional structure)

4. **D**: "long" → should be "longer" (comparative form)

For the second sentence:

1. **A**: "Streets will be" → should be "Streets will become" (more appropriate verb)

2. **B**: "cleaner if" → no mistake here (correct)

3. **C**: "people put" → should be "people put rubbish" (clarity)

4. **D**: "in a rubbish bin" → no mistake here (correct)

If you need more specific corrections or details, feel free to ask!