Many Bacteria Do Not Interact with Humans, but Those That

Many bacteria do not interact with humans, but those that do can always be classified as either harmful or not harmful to humans. True or False?

A) False. Some get worse as they age.
B) True. They always either hurt us or they don't.
C) False. No bacteria species is always bad for us all the time.
D) True. Once they mutate to be harmful, they stay that way.
E) False. Some are fine in small numbers, but in big numbers they can overwhelm the immune system and cause problems.