Write the Expression with Only Positive Exponents $(-\mathrm{a})^{-18}$ A) $\frac{1}{-a^{18}}$ B) $18 \mathrm{a}$

Multiple Choice

Write the expression with only positive exponents. Assume all variables represent nonzero numbers. Simplify if necessary.
- $(-\mathrm{a}) ^{-18}$

A) $\frac{1}{-a^{18}}$

B) $18 \mathrm{a}$

C) $\frac{1}{a^{-18}}$

D) $\frac{1}{a^{18}}$