Refer to the Graphic Below

Refer to the graphic below.Why is the progression of uranium-238 to the stable lead-206 such a concern?

A) There is no guarantee that the uranium-238 will progress in this manner,so it might become something even more dangerous.
B) The long length of time it takes for uranium-238 to become harmless means it is difficult to dispose of in a safe manner.
C) Uranium-238 is the quickest of the radioactive elements to decay; the others are even more dangerous.
D) Uranium-238 is the most reactive of the uranium isotopes and so is the most dangerous.
E) Uranium-238 is the least common of the uranium isotopes and so is the hardest to find.