If an Isotope's Half-Life Is 100 Years

If an isotope's half-life is 100 years,

A) in 50 years, only half of the atoms in a sample of that isotope will remain.
B) in 100 years, only half of the atoms in a sample of that isotope will remain.
C) in 200 years, only half of the atoms in a sample of that isotope will remain.
D) that isotope will no longer exist in 200 years.
E) that isotope will no longer exist in 50 years.