Answer:
b) bacteria
Explanation:
Bacteria carry out nitrogen fixation.
a) is wrong. The bacteria in the root nodules fix the nitrogen.
c) is wrong. Carnivorous plants get nitrogen directly from the insects they capture. For most plants, insect nitrogen comes from the action of microorganisms on the dead insects.
d) is wrong. Lightning can fix nitrogen, but plants obtain the vast majority of their nitrogen from bacteria.
