Half life question: The table below shows the initial and final masses of a radioactive material whose half-life is 15 years. Initial mass (in kilograms) 0.8
Final mass (in kilograms) 0.05

Based on the table, which of these conclusions is correct?
A) The material decayed from 0.8 kilograms to 0.05 kilogram in 60 years.
B) The material decayed from 0.8 kilograms to 0.05 kilogram in 30 years.
C) The mass of the material was 0.1 kilograms after four half lives.
D) The mass of the material was 0.1 kilograms after five half lives.