Loss of Biodiversity Matters Not Only with Regard to Mammals

Loss of biodiversity matters not only with regard to mammals or other vertebrates, but also to microbes. Which of the following best explains the importance of discovering and protecting microbes from extinction?

A) Microbes play a role in digestion.
B) Microbes may produce unique proteins useful in genetic research.
C) Microbes are much greater in species number than any other taxa on Earth.
D) Microbes may be the most sensitive to the next large extinction event.