Answer:
A = Activator
B = Effector
Explanation:
An activator is a protein which typically binds to a short (50–1500 bp) region of DNA which might be located either upstream (mainly) or downstream of a gene so as to cause increased transcription. This particular region of DNA is known as enhancer and activator is also  known as transcription factor. Activator is a trans-acting factor which binds to the cis-acting factor which is enhancer so as to enhance transcriptional expression. 
But another protein named as effector may restrict activator from binding to the enhancer leading to a decrease in transcriptional expression by binding to the activator allosterically. Allosteric binding of effector to the activator causes conformational change in activator so it can no longer bind the enhancer. 
 
        
             
        
        
        
Oxygen evaporates from the water
        
             
        
        
        
Answer:
B. methane
Explaination: ...............................
 
        
             
        
        
        
Answer:
The answer is mitochondria.
I hope this helps you
 
        
             
        
        
        
Answer:
What if xylem were only located in the roots and stems, would fluids still move? No because xylem have stoma that enables transpiration to happen. If you remove xylem, you've removed that "vacuum" that pulls that water upward
Explanation: