The correct answer is C. Here's why:
Choice A is illogical. A single experiment does not confirm a theory as true. Multiple successful trials are needed for one to even consider a hypothesis to be accepted as a theory.
Choice B is wrong. If a scientist finds a new way to test a hypothesis, experimental methods do change. Note that when there are additional ways to test a hypothesis, a scientist should test it with additional methods.
Choice D is incorrect. If someone finds a way to test a new hypothesis, it would not be made into law since there is more information regarding the theory. This means that it would remain a theory until one can prove that it can't be tested using different methods.