Select the correct combinations or statements about characteristics of certain organisms.

$\left(\mathrm{a}\right)$ Methanogens are archaebacteria which produce methane in marshy areas.

$\left(\mathrm{b}\right)$ Nostoc is a filamentous green algae which fixes atmospheric nitrogen.

$\left(\mathrm{c}\right)$ Chemosynthetic autotrophic bacteria synthesize cellulose from glucose.

$\left(\mathrm{d}\right)$ Mycoplasma lacks a cell wall and pathogenic to plant as well as animal.