Answer:
 Environmental Scientists can use GPS tagging
Explanation:
 
        
                    
             
        
        
        
The answer is single opening. The gastrovascular cavity varies from the alimentary canal in that only the gastrovascular cavity has only a single opening. In addition, an alimentary canal has two openings and food moves over it unidirectional. The gastrovascular cavity is a construction establish in primitive animal phyla. It is accountable in cooperation with the digestion of food and the transportation of nutrients all over the body.
        
             
        
        
        
Answer:
3 ways to understand the differences between compounds and mixtures are described below in explanation.
Explanation:
1. In a mixture, no new product is formed. It is a simple tacking of two molecules without any chemical reaction occurring. For example water and sand. Compound is a new substance formed by chemical reactions occurring between various molecules. For example, carbon and oxygen combine to form carbon dioxide.
2. A compound is always homogeneous whereas a mixture can be homogeneous or heterogeneous.
3. Compounds have a fixed boiling and melting temperature. Whereas, mixtures do not have a definite melting and boiling temperature. 
 
 
        
             
        
        
        
Water molecule, skin cell, E. Coli Bacteria, grain of salt, human
        
             
        
        
        
I think it stands for Gap. Do you mean G1 and G2 interphases?