Answer:
B. one fourth of the original substance
Explanation:
a substance's half life is how long it takes for half of the atoms in the substance to chemically decompose. once it's half life has been completed, it will start again with the remaining material. after 6000 years, only half of the material will remain, after 12,000 years a quarter wil remain, after 18,000 years an eighth will remain, etc.
