<span>A fast-flowing river of air that forms when two air masses of very different temperatures meet is called a jet stream :)</span>
        
                    
             
        
        
        
Hello,
Here is your answer:
The proper answer to this question that it "can take more than <span>thousands of years for the process to be completed"!
If you need anymore help feel free to ask me!
Hope this helps!</span>
        
             
        
        
        
A dichotomous key helps you identify unknown specimens based on their traits because there are only two options available per trait. Selecting one from the two options (usually contrasting characteristics) from each step leads to smaller and smaller groups until the option is reduced to single and unique trait of an organism. 
Considering you need to identify an organism. So, on the top of they key is animal with options: (a) with red blood cells and (b) no red blood cells. The option you will select is no red blood cells and under option b, you’re given two choices again: (a) hard bodies and (b) soft bodies. You’ll select soft bodies, then two options again are given: (a) with shell and (b) without shell. The option you’ll select would be without shell, and so on.
        
                    
             
        
        
        
I think it's the simple columnar epithelium.