Which one all of the or what
        
                    
             
        
        
        
Explanation:
respiration because it's about blood circulation 
 
        
             
        
        
        
Answer:
Electron microscope would be used for if, 
C) details of cell structures needed to be distinguished.
Explanation:
- The general principal of electron microscopy is analogous to light microscopy except that it uses electrons to analyse the specimen instead of light.
 - Electron microscopy focuses a beam of electron on the target sample and records the difference in absorption by different surfaces.
 - Electron microscopy is used to get the detailed structure of cells and surface features of various viruses and bacteria.
 - However, it is not possible to view living biological samples through electron microscope because high velocity electron have immense energy to kill living cells.
 - These samples are thus, fixed and then viewed.