Answer:
The correct option is A) microscope
Step-by-step explanation:
A microscope can be defined as an instrument which enables the naked eye to see objects which cannot be seen otherwise. The advancements in microscopy have enabled humans to have a look at the tiniest of organisms. Before microscope, only those organisms which were visible to the naked eye were considered to be living things. But the discovery of microscope showed humans that there are tiny organisms present on Earth which are living but they cannot be seen with the naked eye.