Why Do Some Plants,like Beans and Peas,contain Bacteria in Compartments

Why do some plants,like beans and peas,contain bacteria in compartments in their roots?

A) These friendly bacteria help the plant fight off disease-causing bacteria in the soil.
B) These bacteria are capable of nitrogen fixation and will provide the plant with nitrogen in exchange for carbohydrates.
C) Peas and beans form these compartments in their roots to block these bacteria from infecting the rest of the plant.
D) These bacteria increase the efficiency of root hairs' absorption of water.