Answer:
Lower esophageal sphincter
Explanation:
The biological valves are the muscular structures composed of the smooth muscles which form thick tubular structure to allow the controlled movement of any material through it. The valves in the digestive system are known as the sphincters.
The sphincters control the unidirectional movement of the eaten food, chyme and the bolus in the digestive tract.
A sphincter is present at the lower portion of the oesophagus (food pipe) which contracts to prevent the backflow of the food from the stomach and since the sphincter is present at the lower side of the oesophagus, therefore, is known as the lower esophagal sphincter.
Thus, Lower esophageal sphincter is correct.
 
        
             
        
        
        
 Protection for the head is needed in cases of direct collision sports like hockey and football. Collisions with another player or the turf may result in a concussion, thus all the helmets must possess NOCSAE certifications.  
The helmet should fit comfortably around all the segments of the player's head, there should be no gaps between the head and pads. It should cover the base of the skull, the pads positioned at the back of the neck should be comfortable, and at the same time should not be uncomfortable.  
The helmet should not come down over the eyes, the front edge of the helmet should be 3/4 inch or of two finger widths above the eyebrows.
 
        
             
        
        
        
Answer:
sunlight
Explanation:
plants need sunlight to survive and therefore when it is indoit's it doesn't receive sunlight
 
        
                    
             
        
        
        
Answer:
The fertility factor or the F factor signifies a plasmid in some bacteria, which allows the conduction of genetic substance from a donor cell to the recipient by the process of conjugation, leading to recombination.  
The genotypic difference between the F- cells, F+ cells, and the Hfr cells are that the F- cells are devoid of the F factor, the F+ cells possess autonomous F factor, that is, a segment of DNA, which can replicate autonomously in the cell. In case of Hfr, the F factor is integrated into its chromosomal DNA, thus, they carry an integrated F factor.  
 
        
             
        
        
        
He should be able to smoke because 1. he was off campus and 2. he's 18 which is a legal adult 3. there's no policy stating he can't do such