[单选题]
The Sun has apparent /u c/0f1v; jh lt(wo(m,vagyvbrightness s6434f 39 ytyxyk pndsat 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. $0.00063 \; B$
