Answer:
A shallow
Explanation:
Something that is described as shallow is "of little depth". The initial description given of the canal is that of a body of water that  was not deep enough to allow the passage of large ships. To solve this problem of the canal being shallow, dredgers had to be used to reach the bottom of the canal, thus increasing the depth of the canal. 
After this was done, an improvement was seen in the increased number of ships plying the canal water body. 
 
        
             
        
        
        
A bigwig refers to a person who is an expert in a particular area of study or field. Thus, a bacterial wig will be someone who is an expert in the area of bacteriology. Such a person will probably have the highest degree that is obtainable in that field and will be an authority to reckon with when it comes to the issue of bacteria. 
        
                    
             
        
        
        
Mohan will have written the letter
 
        
             
        
        
        
Answer:
1,3, and 4.
Explanation:
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