Find the Linear Approximation To $f ( x ) = e ^ { - 3 x }$

Find the linear approximation to $f ( x ) = e ^ { - 3 x }$ at a = 0.

A) 1 + x
B) 1 + 3x
C) 1 - x
D) 1 - 3x
E) 3 + 3x
F) -3x
G) 3 - 3x
H) None of these