Answer:
The ability of sequences within the leader mRNA to pair with one another and form stem-lopp structures
Explanation:
A form of feedback regulation controls the  trp operon by regulating transcription termination, a mechanism referred to as Attenuation. 
-In the presence of high concentrations of tryptophan, RNA polymerase ceases transcription  shortly after initiation in a region called the leader sequence.
-If  the concentration of tryptophan is low, transcription does not  terminate until the entire operon is transcribed. The mechanism of attenuation links alternative RNA secondary structures  to transcription termination. 
-Immediately after transcription,  RNA from the leader region folds into one of two alternative  secondary structures. 
-One of these structures is a transcription  termination signal that stops RNA polymerase from continuing  to the end of the operon. 
-The alternative structure does not  contain a transcription termination signal and allows transcription of a single mRNA that encodes all the structural genes.  
-The decision as to which of the two alternative RNA structures  formed is regulated by the concentration of tryptophan.
 
        
             
        
        
        
 A chain of amino acids folded and twisted into a molecule
 
        
             
        
        
        
Answer:
F
Explanation:
They share a more recent common ancestor
 
        
             
        
        
        
Answer:
The answer you are looking for is A.