Answer:
Option D, Anabaena
Step-by-step explanation:
Some filamentous cyano bacterias during nitrogen starvation produces heterocysts which are specialized cells that are capable of fixing nitrogen.
Some common example of these bacteria's are - Cylindrospermum , Anabaena and Nostoc etc.
Anabaena fix the nitrogen in the vegetative cell through a filament under aerobic conditions when there is lack of fixed nitrogen either Ammonia or nitrate.
Hence, option D is correct.