Answer:
D the train
Explanation:
The train is safe very fast and was the first built
 
        
                    
             
        
        
        
A. oxygen atom
H2 O1
There are 2 hydrogen atoms and 1 oxygen atom
        
                    
             
        
        
        
Answer:
 the answer is carbohydrate
 
        
                    
             
        
        
        
Answer:
d. secondary endosymbiosis.
Explanation:
- When a living cell acquires another organism that eventually becomes a part of this cell, this process is known as primary endosymbiosis.
- When an organism that has already undergone primary endosymbiosis engulfs another eukaryotic organism then this process is known as secondary endosymbiosis. 
- Secondary endosymbiosis has been known to occur in plastids because of which they are surrounded by two membranes. This bilayer is present because one of the layers is the original outer membrane of the organism and the other membrane is that of the organism that has been engulfed. 
 
        
             
        
        
        
All eukaryote cells lack a nucleus