Messenger RNA (mRNA) molecules carry the coding sequences for protein synthesis and are called transcripts; ribosomal RNA (rRNA) molecules form the core of a cell's ribosomes (the structures in which protein synthesis takes place); and transfer RNA (tRNA) molecules carry amino acids to the ribosomes during protein synthesis. In eukaryotic cells, each class of RNA has its own polymerase, whereas in prokaryotic cells, a single RNA polymerase synthesizes the different class of RNA. Other types of RNA also exist but are not as well understood, although they appear to play regulatory roles in gene expression and also be involved in protection against invading viruses.
 
        
                    
             
        
        
        
Biosphere, relatively thin life-supporting stratum of Earth's surface, extending from a few kilometres into the atmosphere to the deep-sea vents of the ocean.
        
             
        
        
        
Fungi lacks the ability to produce their own food because they do not have chloroplast which is needed to obtain energy from the sun and convert it into food. Also fungi lack ability to fix nitrogen which has to be incorporated into their food. They also can not fix carbon and utilize it to produce food. Because of these they have to depend on dead organic matters for food.
        
             
        
        
        
Rigid skeletons are formed from materials including chitin (in arthropods), calcium compounds such as calcium carbonate (in stony corals and mollusks) and silicate (for diatoms and radiolarians).
 
        
                    
             
        
        
        
Answer: Liver 
Explanation:
The hepatic portal system of liver connects the capillaries of the gastrointestinal tract to the liver. The nutrient rich blood from the gastrointestinal tract reaches the liver.
The blood that is returned back to the heart is first bought to liver and then it is returned back to the heart.
From the liver after processing the blood goes into heart for further processing.
Hence, the correct answer is option d