D) the last one bc water goes in and make electrical power
Heterocyst-forming cyanobacteria differentiate highly specialized cells to provide fixed nitrogen to the vegetative cells in a filament. In the presence of a source of combined nitrogen such as nitrate or ammonium, Anabaena PCC 7120 grows as long filaments containing hundreds of photosynthetic vegetative cells.
The correct option is c. (20 m) .
As the formula to calculate wavelength is :
wavelength = wavespeed / frequency