Express the Radical in Simplified Form $\sqrt[4]{81 a^{4}}$ A) $3 a^{2}$ B) $81 \mathrm{a}$

Multiple Choice

Express the radical in simplified form.Assume that all variables represent positive real numbers.
- $\sqrt[4]{81 a^{4}}$

A) $3 a^{2}$
B) $81 \mathrm{a}$
C) $3 a$
D) $3 \sqrt{\mathrm{a}}$