Simplify the Complex Number and Write It in Standard Form $3 i ^ { 2 } - 7 i ^ { 3 }$

Simplify the complex number and write it in standard form.
$3 i ^ { 2 } - 7 i ^ { 3 }$

A) $- 7 + 3 i$
B) $3 + 7 i$
C) $- 3 - 7 i$
D) $- 3 + 7 i$
E) $3 - 7 i$