Simplify the Radical Expression $\sqrt { \mathrm { m } ^ { 21 } \mathrm { n }^{ 12} }$

Multiple Choice

Simplify the radical expression. Assume all variables represent nonnegative real numbers.
- $\sqrt { \mathrm { m } ^ { 21 } \mathrm { n }^{ 12} }$

A) $\mathrm { m } ^ { 10 } \mathrm { n } ^ { 6 }$
B) $m ^{10}n^ 6 \sqrt { m }$
C) $\mathrm { m }^{ 10} \mathrm { n } ^{12} \sqrt { \mathrm { m } }$
D) $\mathrm { m } ^ { 11 } \mathrm { n } ^7$