Answer:
UV Radiation and smoking? 
Explanation:
 
        
                    
             
        
        
        
20 Amino acids is the answer
        
             
        
        
        
Does that mean in order? if not the answer is C
        
             
        
        
        
Answer;
-Neurotransmitters.
One of the first key terms she memorizes is neurotransmitters because these are the chemicals via which neurons communicate with each other.
Explanation;
-Neurons communicate with each other via electrical events called 'action potentials' and chemical neurotransmitters. At the junction between two neurons (synapse), an action potential causes neuron A to release a chemical neurotransmitter.
-Neurons are connected to each other through synapses, sites where signals are transmitted in the form of chemical messengers.
 
        
             
        
        
        
Oof, the answer is OOF!!!!!