Answer:
The correct option is A) microscope
Step-by-step explanation:
A microscope can be defined as an instrument which enables the human eye to see objects which are otherwise not visible to the naked eye. Before the discovery of microscope, scientists did not know that there might be other living organisms other than plants and animals. The microscope enabled the human eye to see other living things which are not visible to the naked eye but carry out the life processes. Hence, option A is the correct answer.