Answer: D
Explanation: just did it on edg 
 
        
             
        
        
        
Carbon is the atom, which is necessarily find in the living organism. 
All the living organisms are made up of biomolecules. All the biomolecules are organic compounds. The substance cannot be consider as living, if it lacks nucleic acids. There are two types of nucleic acids DNA (deoxyribonucleic acid) and RNA (ribonucleic acid), both have a structure made up of carbon rings and chains.
Other than nucleic acids, proteins, enzymes, hormones etc are also made up of carbon. So, all the living cells, or dead remain of organism must have carbon atom.
Hence, the correct answer is option D. carbon.
 
        
             
        
        
        
Answer:
The above paragraphs describes that how salt- and fresh-water fish regulates their osmoregulation. Hence, the correct answer would be c. have adapted to deal with osmosis.
Osmosis is the process by which solvent's molecule move from region of low concentration (hypo-tonic) to the region of high concentration (hyper-tonic) through a semi-permeable membrane. 
In sea-water fishes, the body fluids are hypo-tonic to the surrounding water and thus water is kept moving out of their gills. In order to prevent the excess water loss they need to drink water constantly and excrete concentrated urine.
In contrast, fresh-water fishes body fluids are hyper-tonic to surrounding water and hence, water keeps entering in their body through gills. So, in order to prevent excess dilution they absorb salt from surrounding with the help of gills and also their bodies reabsorb salt from urine. 
 
        
                    
             
        
        
        
The glomerulus hydrostatic pressure.