Which of the Following Statements Is True

Which of the following statements is true?

A) Neurotransmitters are less likely to be considered contributors to mental disorders than psychological factors
B) The reuptake and degradation processes influence the levels of neurotransmitters
C) Substances such as heroin, cocaine, and amphetamines have little effect on neurotransmitter levels
D) Scientists have identified more than 1000 different neurotransmitters