Firmicutes have contrasting approaches to reproduction. Select an approach for a firmicutes that inhabits a place where substrates will run out and require relocation to the GI track allowing the microbe to access substrates and start vegetative growth again (like a rodent's GI tract):
a. Multisporulation as in Metabacterium polispora
b. One reinforced endospore as in Bacillus subtilis
c. Internal cell division as in Epulopiscium fishelsoni
d. Highly motile arthrospores as in the case of Streptomycetes

b. One reinforced endospore as in Bacillus subtilis

Explanation:

The Firmicutes are a phylum of bacteria, most of which have gram-positive cell wall structure. A few, however, such as Megasphaera, Pectinatus, Selenomonas and Zymophilus, have a porous pseudo-outer membrane that causes them to stain gram-negative.

Metabacterium polyspora is an unusual multiple endospore-producing bacterium isolated from the cecum of guinea pigs. This bacterium is physically similar to the phylogenetically related surgeonfish intestinal symbiont Epulopiscium fishelson.

Epulopiscium spp. are a group of Gram-positive bacteria that have a symbiotic relationship with surgeonfish. These bacteria are known for their unusually large size, many ranging from 200–700 μm in length.

Streptomyces is the largest genus of Actinobacteria and the type genus of the family Streptomycetaceae. Over 500 species of Streptomyces bacteria have been described. As with the other Actinobacteria, streptomycetes are gram-positive, and have genomes with high GC content.

Bacillus subtilis, known also as the hay bacillus or grass bacillus, is a Gram-positive, catalase-positive bacterium, found in soil and the gastrointestinal tract of ruminants and humans.