Why Have Some Plants Evolved Mutualistic Relationships with Nitrogen-Fixing Bacteria

Multiple Choice

Why have some plants evolved mutualistic relationships with nitrogen-fixing bacteria?

A) The bacteria transform nitrogen into forms useful forms for the plants; the plants provide water and a place for the bacteria to live.
B) The bacteria protect the plant from harmful effects of nitrogen compounds such as ammonia; the plants provide carbohydrates for the bacteria.
C) The bacteria utilize nitrogen to produce energy for the plants; the plants provide the source of the nitrogen for the bacteria.
D) The bacteria provide natural immunities to the plants; the plants shelter the bacteria from predators.