Answer: She developed the idea that there were more radioactive substances than uranium.
Step-by-step explanation:
In the given problem, the Curies took pure uranium and a uranium-containing substance. When they measured the amount of radioactivity, there was more in the uranium-containing substance than the pure uranium.
She extracted uranium from an ore. She surprised to find that the leftover ore showed more activity than pure uranium. The ore contained other radioactive elements.
She likely to develop the idea that there were more radioactive substances than uranium.