Pls pls pls quick (explanation too)
major scientific theories include the cell theory, the big bang theory, and the theory of plate tectonics. how are scientific theories formed?

a. through a single scientific discovery in which a scientist learns something new b. through the formation of several related hypotheses
c. through meetings between scientists in which they discuss several possible answers to a scientific question
d. through extensive testing and the accumulation of several lines of evidence