Here are the correct answers for each blank in the passage:

1. **B. role** - "It is undeniable that each person can play an important role..."
2. **C. considered** - "Cars are considered to be a major source..."
3. **A. air** - "Their exhaust gases contaminate the air..."
4. **B. contaminate** - "...ranging from carbon dioxide as it contaminates..."
5. **A. as** - "...spectrum of unburnt carbon."
6. **D. light** - "...using their own light only in rare cases..."
7. **C. protect** - "...people would be able to protect the environment."
8. **B. recycle** - "...available to individuals is recycling."
9. **B. from** - "...from entering and contaminating waterways..."
10. **B. water** - "...conserve drinkable water and its inhabitants."

So the answers are:
1. B
2. C
3. A
4. B
5. A
6. D
7. C
8. B
9. B
10. B