Streptomyces Are Aerobic Soil Bacteria That Produce Over Two-Thirds of Our

Streptomyces are aerobic soil bacteria that produce over two-thirds of our antibiotics of natural origin.Why might a bacterium produce antibiotics?

A) to allow it to break down the cell walls of plants
B) to protect itself from a host immune system
C) to kill competing bacteria of the same species
D) to kill viruses that may try to infect it
E) to kill competing bacteria of different species