The correct answer is a) most viruses cannot be seen with a light microscope.
Explanation: Viruses are incredibly small infectious agents, typically ranging from 20 to 300 nanometers in size. Due to their tiny size, they cannot be viewed using a standard light microscope, which has a resolution limit of about 200 nanometers. Instead, scientists use electron microscopes, which provide much higher magnification and resolution, to observe viruses.
Option b) is incorrect because viruses are not prokaryotic; they lack a cellular structure and are classified as acellular. Option c) is also incorrect since viruses do not contain ribosomes at all, whether 70S or any other type, as they do not carry out protein synthesis on their own. Lastly, option d) is not applicable because viruses do not replicate through binary fission, which is a method used by prokaryotes. Instead, viruses invade a host cell and hijack its machinery to reproduce.