The correct option is C Hypothesis
The term hypothesis means a proposition or a set of propositions set forth as an explanation for the occurrence of some specific phenomenon. In this case, the phenomenon was smallest constituent entity of living organisms. In 1838, German Botanist Matthias Schleiden found that all plant tissues are made up of cells which have essentially similar structure. German zoologist Theodor Schwann, 1839, working independently observed that animal cells do not have cell wall but are otherwise similar among themselves. Thus, the original idea of both the workers was a hypothesis based on their observation which had to be experimentally verified by other workers.