Why Were the Advent of Metagenomics,and the Application of Molecular

Why were the advent of metagenomics,and the application of molecular techniques such as single-cell and next-generation sequencing,important for defining a microbial relationship?

A) Newer methods revealed that symbiotic relationships exist between a host and one to thousands or more microorganisms,challenging the former definition of a symbiotic relationship as one that occurs between a single microbe and its host.
B) Newer methods revealed that symbiotic relationships exist between a host and only one microbe,challenging the former definition of a symbiotic relationship as one that occurs between thousands to trillions of microbes and its host.
C) Microbiologists originally defined symbiotic relationships as those existing only between bacteria and animal hosts; the advent of newer methods broadened the definition of a host to include organisms other than animals.
D) Microbiologists originally defined symbiotic relationships as those that were parasitic,where the microbe harmed the host; the advent of newer methods broadened the definition of symbiosis to include mutualistism and commensalism.