Step 1: Link potential to position.
In a uniform field pointing along the horizontal, the potential only depends on the horizontal position $x$. \[ V = -E x \] So points at the same $x$ have the same potential.
Step 2: Look at points A and B.
In the figure $A$ and $B$ lie one above the other, so they share the same horizontal position.
Step 3: Compare A and B.
Same $x$ means same potential. \[ V_A = V_B \]
Step 4: Look at points C and D.
These lie along the horizontal direction. Potential drops as we move in the direction the field points.
Step 5: Compare C and D.
Point $D$ is on the higher potential side and $C$ on the lower side, so \[ V_D > V_C \quad\text{that is}\quad V_C < V_D \]
Step 6: Combine both results.
\[ \boxed{V_A = V_B,\; V_C < V_D} \]