Compound light microscopy is used to visualize cells and tissues. what is a major disadvantage with using this technique?

Compound light microscope is an ocular apparatus for forming enlarged images of insignificant organisms. The intensification and tenacity power is inadequate, because viewing light is used which has the minimum wavelength if about 40 nano-meters. And also the lenses of these microscopes tend to be blurry over time if not appropriately maintained. 

i think a) betsy can donate only blood to mark is correct because, mark and betsy have the same blood type. whereas nobody else has b+ blood so betsy can't donate to them.