Which of the following statements regarding the development of cell theory is true? a. cell theory describes a range of phenomena concerning cells, and it is the most well-supported explanation of the basic structure and function of the cell. b. cell theory was first developed in the 19th century, and it has since been replaced by a theory that identifies dna as the basic structure of life. c. cell theory was discarded in the late 20th century because the existence of cells cannot be explained by the theory of evolution. d. cell theory is one of many accepted theories regarding the fundamental structure and function of cells, and it is no longer subject to change.