Transmitted, vertical
A transparent specimen is viewed through a microscope using transmitted light while an opaque object requires vertical illumination.
Transmitted light is the light that passes through an object. Transmitted light microscopy is any kind of microscopy in which the light is transmitted from a source located directly across the specimen from the objective. The light is commonly passed through a condenser in order to focus it on the specimen to obtain very high illumination. After the light passes through the specimen, the image of the specimen moves through the objective lens and later to the oculars where the enlarged image is viewed.
 
        
                    
             
        
        
        
Answer:
The correct answer will be option-D.
Explanation:
In the given question doctor used the scientific method to understand and explain the natural phenomenon.
The scientific method involves various steps like making an observation followed by background research, predicting a hypothesis and performing tests to test the hypothesis. These steps have been performed by the doctor.
After these steps the doctor will analyse the result and reach to the conclusion. This would be followed by publishing the results in a scientific journal where it would be reviewed by the fellow scientists.
Therefore, the next step will be publishing the result and thus option-D is the correct answer.
 
        
                    
             
        
        
        
Decomposers are important in the food web since these break down chemical substances.
        
                    
             
        
        
        
The endosymbiotic theory states that eukaryotic cells might have evolved from prokaryotic cells through a close realtionship.