原题
录音 1
What does the speaker say about serotonin?
AIt typically decreases when a microbiome becomes more diverse.
BIt is a neurotransmitter that can be synthesized by the microbiome.
CIt often increases during the digestion of a meal.
DIt acts as a defense mechanism for the immune system.
正确答案：B
解题思路
老师暂未填写解题思路。