设 D: x^2+y^2le a^2，则 iint limits _(D)sqrt (a^2-x^2-y^2)d delta =() A. (4)/(3)pi a^3 B. (2)/(3)pi a^2 C. (2)/(3)pi a^3 D. pi a^2

$$ 设 $D: x^{2}+y^{2}\le a^{2}$，则 $\iint \limits _{D}\sqrt {a^{2}-x^{2}-y^{2}}d \delta =()$ $$

• A. $$ $\frac {4}{3}\pi a^{3}$ $$
• B. $$ $\frac {2}{3}\pi a^{2}$ $$
• C. $$ $\frac {2}{3}\pi a^{3}$ $$
• D. $$ $\pi a^{2}$ $$