Both deletions and insertions occur during the evolution of microbial genomes. Insertions bring in new genes that may be useful for the cell, but deletions A) may increase fitness of a microorganism by eliminating unneeded genes. B) always result in a severe loss of fitness for the microorganism. C) are uncommon because they are usually lethal. D) always result in a severe loss of fitness but keep microbial genomes compact.