The correct answer is: Heartburn often results when the gastroesophageal sphincter fails to close properly.
The gastroesophageal sphincter is a muscle located at the bottom of the esophagus that has to be relaxed in order to allow food to flow down into the stomach. After it contracts (tightens), the food and the stomach acid can’t flow back up into the esophagus.
When the gastroesophageal sphincter fails to close properly acid reflux occurs and causes the heartburn.
 
        
             
        
        
        
The rigth answer is D.
The wavefront or wavefront is an equal phase surface of a wave, i.e., these points have the same travel time from the source. The concept is used to describe the propagation of waves such as sound or electromagnetic radiation (light, radio waves, etc.). In a homogeneous and isotropic medium, in which the waves propagate without deformation, two types of particular waves are distinguished according to whether the wavefronts are spheres (spherical wave) or planes (plane wave).
 
        
                    
             
        
        
        
Explanation:
As The Cell To Divide The Cell Make a Copy that make an Chromosome 
The Chromosome are Called Sister Chromatids . The Sister are identical to the one another and are attracted to each other by Proteins Called Cohesins
 
        
             
        
        
        
1st conclusion: Organisms inherit two copies of each gene, one from each parent.
2nd conclusion: Organisms donate only one copy of each gene in their gametes.
Thus the two copies of each gene segregate or separate during gamete.
Hope this helpedXD