Answer : Option B) Cell theory has been unchanged for many decades and as a result can be accepted as fact.
Explanation : As cells are basic units of life and all the living beings are made up of cells, this was correctly defined by the cell theory. This theory is since its discovery not changed for many decades and is widely accepted as a fact too.
The answer is NOT (B) for anyone looking at this. Got it wrong..
The Answer is: Cell theory has been unchanged for many decades and as a result can be accepted as fact.
The right answer is B.
Theodor Schwann, a doctor of medicine and a German biologist, proposed in a note of 1839 that all living beings are made up of a set of building units of the same type, the cells. This idea was to prove most fruitful: the functioning of all living beings could now be analyzed in the same terms since the unity of construction was common. Despite its many errors and imperfections, especially on the formation of cells, Schwann's theory was to give birth to a unifying synthesis which constitutes in biology, in the same way as the atomic theory in physico-chemistry or that of the big bang in astrophysics , one of the strongest foundations on which science rests.
Cell being the basic unit of life is the main idea of the cell theory because this has been thoroughly studied, observed and believed by many researchers and scientists for a very long time thus, can already be considered as fact unless proved otherwise.