Researchers have identified approximately neurotransmitters.

The answer is more than 100, because base on the research, they have identified more than 100 of the neurotransmitters to be belong in the five groups and they are namely the following, gases, biogenic amines, amino acids, acetylcholine and neuropeptides.

tbh idk same thing here

answer; /// i believe the correct answer is (when one group has an extremely high score at pretest;