x or y because both can cause it 
 
        
             
        
        
        
Answer:
a. establishment of left-right asymmetry
Explanation:
- Cardiac looping is the process in which the heart transforms itself from a straight embryonic heart into a loop that is wounded helically. 
- The looping of the heart takes place on the 23rd day of development.
- As a result of this looping, there is bending of the cranial portion of the heart to the towards the right end and the caudal portion of the heart towards the left end.
- At the end of this looping the atrium takes up a dorsal and cranial position and the ventricle is displaced towards left.
- Thus, the outcome of looping is the establishment of left-right asymmetry.
 
        
             
        
        
        
The answer to the question "When a part rusts is becomes heavier or lighter?" is the rust actually has a tendency to flake off. But as long as the rust is still on the nail, the nail will be heavier. The reason is that you are actually adding an oxygen and hydrogen to the nail.