To achieve a vertical asymptote at \( x = -3 \) using the natural logarithm function \( f(x) = \ln(x) \), we need to adjust the argument of the logarithm.
The logarithm function \( \ln(x) \) has a vertical asymptote at \( x = 0 \). To shift this vertical asymptote to \( x = -3 \), we must adjust the input to the logarithm function such that it becomes zero when \( x = -3 \).
This can be done by using the expression \( x + 3 \) inside the logarithm:
\[ g(x) = \ln(x + 3) \]
With this transformation, the function \( g(x) \) approaches negative infinity as \( x \) approaches \(-3\) from the right, which creates the desired vertical asymptote.
Thus, the correct answer is:
D. \( g(x) = \ln(x + 3) \).