If cells were a school building the cell membrane would be represented by which of the following

either the walls, or the sro (school resource officer), or whatever yall use to limit what comes in and out

The critical mass of a fissionable material depends upon its nuclear properties (specifically, the nuclear fission cross-section), its density, its shape, its enrichment, its purity, its temperature and its surroundings.
i hope this helps. if it does please mark brainliest.