Final answer:
The light microscope is the best choice for observing living microorganisms because it uses visible light and doesn't require specimen preparation that would kill the cells, unlike electron microscopes.
Step-by-step explanation:
The correct type of microscope for observing living microorganisms is C) Light microscope. Unlike electron microscopes, which require a vacuum and often kill the specimen during preparation, light microscopes use visible light and can visualize living cells. However, when using a light microscope, individual cells are usually transparent, and their components are not easily distinguishable unless they are stained with special stains. This staining process generally results in the death of the cells. As such, various adaptations of light microscopy, such as phase-contrast microscopy or darkfield microscopy, are employed to enhance contrast without staining, thus allowing the observation of living organisms.
For viewing thick structures like biofilms, the d. confocal scanning laser microscope could be especially useful as it allows for the detailed observation of specimens that are thicker than the typical single-celled organisms observed with standard light microscopy.