Which of the following expressions correctly describes Completing the Square?

The expression that correctly describes completing the square is;
Option C; x² + ax + (a/2)²
Let's say we have an expression;
x² + ax + c = 0
Let us first rearrange to get;
x² + ax = -c
Add (a/2)² to both sides to get;
x² + ax + (a/2)² = -c + (a/2)²
Thereafter, we can simplify the left hand side to give; (x + a/2)² = -c + (a/2)²
But from the given options, the only one with a corresponding step with what we have is option C which is x² + ax + (a/2)²
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