The Wronskian of the Functions $e ^ { x }$ And $e ^ { 3 x }$

Multiple Choice

The Wronskian of the functions $e ^ { x }$ and $e ^ { 3 x }$ is

A) $2 e ^ { 4 x }$
B) $- 2 e ^ { 4 x }$
C) $2 e ^ { 2 x }$
D) $4 e ^ { 4 x }$
E) $4 e ^ { 2 x }$