Marie Curie formulated the hypothesis that there exists a radioactive element distinct from uranium and barium, and she tested its implications. Her method was first applied to pitchblende, a substance that includes uranium and gives off high amounts of radioactivity. Curie isolated a white powder from the pitchblende that was 900 times more radioactive than pure uranium. But because the powder contained barium, an element that also produces radiation, the findings were not yet conclusive. Curie resorted to spectrographic analysis, which indicated that the substance was not barium. The evidence produced by all of these tests established the existence of another radioactive element that came to be known as radium. Which of the following statements properly describe the discovery of radium? A. Because barium and uranium were the only elements known to give off radiation and yet, in this case, they had to be eliminated as the source of an excess radiation, internal coherence required the hypothesis of an as yet unknown radioactive element.
B. Curie's spectrographic studies contradict the belief that she had discovered a substance that was neither uranium nor barium.
C. Spectrographic studies supported the coherence of the radium hypothesis.
D. The internal coherence of the hypothesis that established the existence of radium was achieved in part by the elimination of other known elements that cause radiation.