increase the efficiency of photosynthesis greater immunity of crops against diseases fewer bacteria in soil and in living organisms more usable nitrogen for other plants
I gave my students this multiple choice question: Which effect would the growing of legume crops such as beans and soybeans have?

Only one answer is correct among these 4 choices:
- increase the efficiency of photosynthesis
- greater immunity of crops against diseases
- fewer bacteria in soil and in living organisms
- more usable nitrogen for other plants

Could you tell me which one is correct?

more usable nitrogen for other plants