Find the Domain Of $x$ In the Expression $\sqrt { 81 - x ^ { 2 } }$

Multiple Choice

Find the domain of $x$ in the expression. Use a graphing utility to verify your result. $\sqrt { 81 - x ^ { 2 } }$

A) $[ - 81,81 ]$
B) $( - 9,9 )$
C) $[ - 9,81 )$
D) $[ - 9,9 ]$
E) $( - 81,81 )$