The correct answer is C. The Buddha believed in the theory of Karma.
Karma is the idea that every action has an equal and opposite reaction. In other words, what you do will come back to you. The Buddha believed that karma is a natural law, and that it is the cause of all suffering. He taught that the way to end suffering is to break the cycle of karma by living a moral life and following the Eightfold Path.
Option A is incorrect because the Buddha did not reject the theory of Karma. He accepted it as a natural law.
Option B is incorrect because the Buddha was not non-committal on the theory of Karma. He believed in it and taught about it.
Option D is incorrect because the Buddha did not suggest an alternative to the theory of Karma. He accepted it as a natural law and taught about how to break the cycle of karma.