The right option is; a. microbiome
The sum total of all the microbes in a certain environment is termed the microbiome.
A microbiome is the sum total (community) of all the micro-organisms that are living together in a certain environment such as in body of humans, animals, plants and in soils. Micro-organisms (microbes) are unicellular organisms that cannot be seen with the naked eyes but can only be seen with the aid of a microscope. Examples of microorganisms include fungi, bacteria, archaea, and protists.
