Step 1: Understand the geometry of the ellipse.
The standard form of an ellipse with its center at \( (h, k) \) and axes parallel to the coordinate axes is:
\[
\frac{(x - h)^2}{a^2} + \frac{(y - k)^2}{b^2} = 1
\]
where \( a \) is the length of the semi-major axis and \( b \) is the length of the semi-minor axis. The foci of the ellipse are located at \( (h \pm c, k) \) if the major axis is horizontal or at \( (h, k \pm c) \) if the major axis is vertical.
Step 2: Analyze the given points.
We are given:
- The center of the ellipse at \( (2, -3) \),
- One vertex at \( (4, -3) \),
- One focus at \( (3, -3) \).
The distance between the center and the vertex is the length of the semi-major axis \( a \), and the distance between the center and the focus is the focal distance \( c \).
Step 3: Calculate \( a \) and \( c \).
The distance between the center \( (2, -3) \) and the vertex \( (4, -3) \) is 2 units, so:
\[
a = 2
\]
The distance between the center \( (2, -3) \) and the focus \( (3, -3) \) is 1 unit, so:
\[
c = 1
\]
Step 4: Use the relationship \( c^2 = a^2 - b^2 \).
For an ellipse, the relationship between \( a \), \( b \), and \( c \) is given by:
\[
c^2 = a^2 - b^2
\]
Substitute \( a = 2 \) and \( c = 1 \) into this equation:
\[
1^2 = 2^2 - b^2 \quad \implies \quad 1 = 4 - b^2 \quad \implies \quad b^2 = 3
\]
Step 5: Write the equation of the ellipse.
Thus, the equation of the ellipse is:
\[
\frac{(x - 2)^2}{2^2} + \frac{(y + 3)^2}{\sqrt{3}^2} = 1
\]
Simplifying:
\[
\frac{(x - 2)^2}{4} + \frac{(y + 3)^2}{3} = 1
\]
Step 6: Conclusion.
Thus, the equation of the ellipse is \( \frac{(x - 2)^2}{4} + \frac{(y + 3)^2}{3} = 1 \), corresponding to option (A).