Which of the following assumptions does radiometric dating make?

(A) The rock has not been in the presence of a strong magnetic field.
(B) The rock formed prior to the time that the radioactive isotope began decaying.
(C) Neither the original isotope nor the decay product has escaped from the rock.
(D) The rate of decay is unpredictable and has greatly changed over time.

Radiometric dating is a scientific technique based on predictable radioactive decay. The age of a rock or other substance that contains trace amounts of radioactive isotopes can be estimated by measuring how much of the original radioactive isotope is present and how much of the decayed version is present. Because the rate of decay occurs in an even, predictable manner, the original creation date of the rock can be estimated.