Multiply the Radical Expressions $( \sqrt { 13 } + x ) ( \sqrt { 13 } - x )$

Multiple Choice

Multiply the radical expressions. $( \sqrt { 13 } + x ) ( \sqrt { 13 } - x )$

A) $\sqrt { 13 } - x ^ { 2 }$
B) $13 + x ^ { 2 }$
C) $\sqrt { 26 } - x ^ { 2 }$
D) $13 - x ^ { 2 }$