Why would Hooke's discovery have been impossible without the invention of the microscope? A. Because all living things are made up of cells. B. Because cells are too small to see without a microscope C. Because cells are the building blocks of life D. Because electron microscope are necessary to see cells

From the question you can immediately infer that it's either B or D, as A and C basically mean the same thing and it isn't anything related to a microscope. I can tell you now that you don't need an electron microscope to see cells, they're only required for the atomic level.

Therefore, the answer is B, as you can't see cells without a microscope but you only need a light microscope, not an electron microscope.