Nitrogen Fixation

Step 1: Recall nitrogen-fixing bacteria.
- Rhizobium: Symbiotic nitrogen fixer found in root nodules of legumes.
- Azotobacter: Free-living nitrogen fixer present in soil.
- Azospirillum: Free-living nitrogen fixer, commonly associated with grasses.
- Streptococcus: A pathogenic bacterium, not involved in nitrogen fixation.

Step 2: Construct the correct set.
Thus, nitrogen-fixing bacteria are (A), (B), and (C).

Step 3: Verify options.
This matches with Option 1.

Final Answer: