Geothermal energy maybe is their answer choices
I thought it was desert biomes, but their biomes are cold at night hot in the day. So, I would say don’t be afraid to ask your teacher. He or She could help you figure it out.
Look up your answer in the first page green box
Answer:
They contain symbiotic rhizobia bacteria within nodules in their root systems, producing nitrogen compounds that help the plant to grow and compete with other plants. When the plant dies, the fixed nitrogen is released, making it available to other plants; this helps to fertilize the soil