The human body has about 10 bacterial cells for every eukaryotic cell. bacteria coat our skin, gut, and mouth. also present are protists, archaeans, and viruses. collectively, these organisms are our microbiota. for most members of our microbiota, our body provides their environment (or space to live). they, in turn, have no effect on us. this is an example of: predation. mutualism. commensalism. an antagonistic relationship.

commensalism

Explanation:

Commensalism is a type of ecological interaction between two species in which one speices benefits while other is unaffected. Commensalism  also can be considered as a type of symbiosis-two species that live together. The interaction between human and its microbiota is beneficial for microbiota while it has no effects on humans.

Although, some bacteria (gut bacteria) can help in digestion. In this case, interaction with human is mutualism (both have benefits).

i'm thinking (a) to keep sand in place; ////////////

explanation: a sand fence or sandbreak, like a snow fence, is used to force windblown, drifting sand to accumulate in a desired place. sand fences are employed to control erosion, sand dune stabilization, keep sand off roadways, and to recruit new material in desert areas.

atp is used for energy.