Explanation:

All the pairs listed are correctly matched in terms of the suitability of biofertilizers for certain crops. Rhizobium is used for leguminous crops like soybean and groundnut due to its ability to fix atmospheric nitrogen when in symbiosis with these plants. Azospirillum is suitable for cereals and millets because it can provide them with the necessary nitrogen and also promote growth by producing plant growth substances. Azolla is a water fern that hosts nitrogen-fixing cyanobacteria and is commonly used in paddy fields, where it doubles as a biofertilizer and as a feed for livestock. Thus, Rhizobium is suitable for Soybean and Groundnut, Azospirillum for Cereals and Millets, and Azolla for Paddy, making all the pairs correctly matched.