The use of bio fertilizer helps in increasing the supply of primary nutrients to plants. Which of the following is/are examples of bio-fertilizers? 1. Azotobacter 2. Rhizobium 3. Azospirillium Choose the correct option.

• A. 1 and 2 only
• B. 1 and 3 only
• C. 2 and 3 only
• D. 1, 2 and 3