The correct option is C a-sheath-protective
b-heterocyst-nitrogen fixation
c- akinete-reproductive cells
Cyanobacteria are filamentous organisms which are covered by a mucilaginous sheath.
Several cyanobacteria have large, barrel shaped, hyaline cells called as heterocysts, which help in nitrogen fixation.
Akinete are called as resting spores which are formed during unfavorable conditions ,where the cell undergoes encystment and becomes thick-walled.