Symbiotic relationship between human/E. coli

E. coli is a bacteria prevalent in human intestines. It produces vitamins, like Vitamin K, for humans, and in turn, we provide it shelter and the nourishment necessary for it to survive. This demonstrates a symbiotic relationship because two species, humans and E. coli, are living in direct and intimate contact with each other. More specifically, this demonstrates mutualism because both species are being benefited from this relationship.

Explanation:

the correct answer is: b. pantala flavescens, because these organisms would have a high level of genetic variation due to sexual reproduction.  

because involves two organisms (parents) whose genetic material combines, sexual reproduction leads to genetic variation in new generations of offspring. the offspring is an unique organism, with new genome, more protected with the higher ability to adapted. this process is fundamental to evolution.