The correct option is B Submicroscopic molecular level
While it is true that a cell is the basic structural and functional unit of life, when it comes to biological organisation, there are groups such as the viruses, each of which cannot be considered as a fully functional cell, and is much smaller than any individual cell. Although a virus lacks most of the basic cell organelles, it possesses the molecular machinery that helps it replicate upon entry into a host organism. Biological organisation, thus, starts at the submicroscopic molecular level.