[单选题]
The mass of Mars, $6.40 \times 10^{23} \; kg$, is about one-tenth that of the Earth, and its radius, 3395 km, is about half that of Earth. What is the mean density of Mars in $kg/m^{3}$?
A. $9.76 \times 10^{2}$
B. $1.95 \times 10^{3}$
C. $3.90 \times 10^{3}$
D. $7.81 \times 10^{3}$
