[单选题]
97.25: Originally there are o a 9whmfm:p, ;fte s8ay 47,b8r(truoNgzkhx ;(6nrv 4 atoms of an unstable isotope. After 20 minutes, only 1/16 of them have notr (xk6n;z4g vh decayed. What is the half life of the isotope?
A. 10 minutes
B. 5 minutes
C. 4 minutes
D. 2 minutes
E. 1 minute
