The E. coli benefit and humans are harmed. There is only a benefit for the humans. There is only a benefit for the E. coli. The E. coli and humans both benefit.
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: The bacteria Escherichia coli (E. coli) live in the intestines of humans and make vitamins such as vitamin K and B-complex vitamins. Which would best describe the relationship between E. coli and humans?
Possibilities:
- The E. coli benefit and humans are harmed.
- There is only a benefit for the humans.
- There is only a benefit for the E. coli.
- The E. coli and humans both benefit.

The E. coli and humans both benefit.