**Explanation:**

When a simply supported beam is subjected to unsymmetrical loading, the deflection would be maximum at a section where the slope is zero. This can be explained by considering the behavior of the beam under the given loading conditions.

**1. Deflection and Slope:**
- The deflection of a beam is the vertical displacement of a point on the beam from its original position.
- The slope of a beam is the angle between the tangent to the deflected shape of the beam and the original horizontal position.

**2. Unsymmetrical Loading:**
- Unsymmetrical loading refers to a loading condition where the load is not evenly distributed on the beam.
- This can result in different bending moments and shear forces acting on different sections of the beam.

**3. Maximum Deflection:**
- The deflection of a beam is influenced by the bending moment and shear force acting on it.
- The bending moment causes the beam to bend, while the shear force causes the beam to shear.
- At a specific section of the beam, the deflection would be maximum if the bending moment and shear force are maximized.

**4. Zero Slope:**
- At a section where the slope is zero, the tangent to the deflected shape of the beam is horizontal.
- This means that the beam is neither bending nor shearing at that section.
- Therefore, the bending moment and shear force at that section would be zero or minimal.

**5. Relationship between Deflection and Slope:**
- The deflection of a beam is directly related to the slope of the beam.
- As the slope increases, the deflection also increases.
- Conversely, as the slope decreases, the deflection decreases.

**6. Maximum Deflection at Zero Slope:**
- Since the deflection is directly related to the slope, the maximum deflection would occur at a section where the slope is zero.
- At this section, the deflection is at its peak value.

Hence, the correct answer is option 'A' - the deflection would be maximum at a section where the slope is zero.