The correct option is D All of these
The widely accepted theory that explains the origin of life is the theory of chemical evolution put forth by Oparin and Haldane. They stated that simple organic molecules are formed from the inorganic constituents. These simple organic monomeric units polymerised to form the complex macromolecules. These macromolecules aggregated and the first non-cellular forms of life could have originated 3 billion years ago as giant molecules consisting of RNA, protein and polysaccharides, etc. The non-cellular life form eventually evolved into the first cellular form of life, about 2000 million years ago.