Answer:
The specimen are placed in vacuum while examining the cells or living organisms. Also, the electron must penetrate inside of the cell and in such conditions, any living organism is not able to survive. Thus, this reason best explains the answer to why dead cells specimen must be used for Transmission electron microscopy.
Explanation:
 
        
             
        
        
        
I think the answer is naturally acquired active immunity..also depends on which disease
        
             
        
        
        
Answer:
<h2>
A
</h2>
Explanation:
1. A channel between two adjacent cells in known as an intercellular cleft.
2. And through these channels many molecules  can easily pass between cells.
3. Importance of Intercellular clefts:
i) It is very important in transportation of fluids and small solutes.  
ii) It contains gap junctions, tight junctions, desmosomes, and adheren proteins and these junctions help in regulate cell communication by signal transduction, surface receptors, or a chemogradient.