Answer:
The answer is B, Cooler materials are highly dense, causing them to sink to the outer core.
Explanation:
 
        
                    
             
        
        
        
<span> Negative staining method is used to view viruses, bacteria, bacterial flagella, biological membrane structures, lipid aggregates and proteins or protein aggregates, which all have a low electron-scattering power. This method is used to view cells or certain organelles of cells more clearly under the microscope in the field of microbiology. </span>
        
             
        
        
        
Answer:
The endomembrane system includes the nuclear envelope.
Explanation:
The endomembrane is composed by the endoplasmic reticulum (ER) and the golgi apparatus. Its main function is to synthesize proteins (rough endoplasmic reticulum studded with ribosomes) proteins can also be modified in the ER of pass to the golgi apparatus where they can be modified and sort to be packed in vesicles to be exported to different parts of the body, for example hormones. 
the nuclear envelope only holds the DNA and it´s not involved in protein synthesis. 
 
        
             
        
        
        
Answer:
It's changeable
Before the microscope, Linnaeus classified organisms only separated in two kingdoms, while more were introduced later. So, they were only classified in two kingdoms, they can be changed and  classified to more than  two.
 
        
                    
             
        
        
        
Community, habitat is in general and ecosystem is the whole place, not just the soil.