[单选题]
The Sun has apparentzm ;snfkwe479v5 u2ip brightness at yq6 x 5mn-goqk+k21uvh ifb60 Earth ($1.5 \times 10^{8} \; km$ away) of B. What would be the apparent brightness of the Sun at Pluto, which is $6.0 \times 10^{9} \; km$ from the Sun?
A. $0.25 \; B$
B. $0.063 \; B$
C. $0.025 \; B$
D. $0.00063 \; B$
