[单选题]
How long would it ta2*m b ds 4tb(kzqpt11zke )y4obyni ,x,.qmzc5h+ f5h l m$4.0 \times 10^{20} \; atoms$ to decay to $1.0 \times 10^{19} \; atoms$ if their half-life was 14.7 years?
A. $29.4 \; years$
B. $58.8 \; years$
C. $78.2 \; years$
D. $147 \; years$
