What did the Curies conclude about radioactivity based on their studies?
A. The amount of radioactivity is an extensive property because it varies as the amount of material varies.
B. The amount of radioactivity is an extensive property because it remains constant as the amount of material varies.
C. The amount of radioactivity is an intensive property because it varies as the amount of material varies.
D. The amount of radioactivity is an intensive property because it remains constant as the amount of material varies.