Choose the One Alternative That Best Completes the Statement or Answers

Multiple Choice

Choose the one alternative that best completes the statement or answers thequestion.
Express in terms of i.
- $\sqrt{-81}$

A) $\pm 9$
B) $\mathrm{i} \sqrt{9}$
C) $9 \mathrm{i}$
D) - $9 \mathrm{i}$