What Is the Significance of the Recent Findings of the Relationship

What is the significance of the recent findings of the relationship between the human microbiome and the nervous system?

A) Some neurotransmitters are synthesized by gut bacteria, and drugs can alter the gut bacteria populations, thereby influencing our health.
B) Gut bacteria species and diversity can have effects on the nervous system that are similar to drug effects.
C) Chronic stress can lead to higher populations of gut bacteria, thereby affecting health.
D) The nervous system responds to gut bacterial populations and helps to regulate their levels.