The Cyanobacteria Found in the Internal Mucilage-Filled Cavities of the Hornworts

The cyanobacteria found in the internal mucilage-filled cavities of the hornworts serve to

A) provide structural support for the plant.
B) produce carbohydrates for the plant.
C) convert atmospheric nitrogen gas into a nutrient form usable by the plant.
D) convert atmospheric carbon gas into a nutrient form usable by the plant.
E) Both c and d