[单选题]
97.25: Originally the - s da)cwah.of+mm,u1srbd0;re mg5-djizp*y/wey u 6 :are N atoms of an unstable isotope. After 20 minutes, only 1/16 of them have not decayed i5ed6pj um-*g:y/ywz . What is the half life of the isotope?
A. 10 minutes
B. 5 minutes
C. 4 minutes
D. 2 minutes
E. 1 minute