20 km (Is correct on grad point)
Correct answer: A). Fission
The cyanobacteria reproduce by the fission. It is a mode of reproduction in which the parent cell divides to give two daughters cell. First of all the circular DNA replicates and then it moves to both the pole of the cell.
After that, the cell lengthens and then the equatorial plate of the cell constricts and divide the plasma membrane into two identical cell
Hence, the correct answer would be option A.