Every seventh time a rat presses a lever, it receives food pallets.
        
             
        
        
        
Answer:
3 & 4 are the right answers.
Explanation:
Profit earned from services, lenders, and investors is the private companies that provide profitable funding options for private healthcare business. They provide money to start a business and they take money back with interests in return. 
On the other hand, government grants and charitable donations provide non-profit healthcare. They provide funds for public benefits.
 
        
             
        
        
        
Cancer cells the branch of medicine concerned with the studying and treatment of tumor.
        
                    
             
        
        
        
Answer:
cell membrane aka membrane
 
        
                    
             
        
        
        
Answer: 
f. Lipoproteins can be distinguished by their densities and composition.
Explanation: Lipoproteins are special particles made up of droplets of fats surrounded by a single layer of phospholipid molecules. Phospholipids are molecules of fats which are attached to a phosphorus-containing group. They are distinctive in being amphipathic, which means they have both polar and non-polar ends.
Lipoproteins are complex particles with a central core containing cholesterol esters and triglycerides surrounded by free cholesterol, phospholipids, and apolipoproteins, which facilitate lipoprotein formation and function.