It has been demonstrated now repeatedly that organic monomers could

According to the modern explanation of Oparin and Haldane hypothesis, the primitive reducing atmosphere of earth was rich in water vapour, carbon monoxide, carbon dioxide, nitrogen and hydrogen. UV light, high temperature and lightening served as sources of energy for chemical reactions between above-mentioned gases to form simple organic compounds such as sugars, amino acids, fatty acids, glycerols and nucleotides. These simple organic compounds were washed from atmosphere to ocean through the rain. They served as monomers for the formation of complex organic compounds in the ocean. Thus, the correct answer is option D.