To identify the step that contains an error using the Commutative Property of Addition in the verification of the equation, let's analyze each step closely.
1. **Step 1**:
- The expression simplifies correctly, collecting like terms.
- \(8 + 4 + x^2 - x^2 + 17x\) is correctly rearranged to \(8 + 4 + 17x + x^2 - x^2\).
2. **Step 2**:
- The left-hand side \(10 + 2 + 10x - 4x^2 + 7x\) is rearranged properly.
- However, notice that on the right-hand side, we have \(10 + 2 + 4x^2 - 4x^2 + 10x + 7x\). The \(4x^2\) and \(-4x^2\) cancel each other out, which makes the right-hand side \(12 + 10x + 7x\) or \(12 + 17x\).
- So, it seems that \(10 + 2 + 4x^2 - 4x^2 + 10x + 7x\) in step 2 is not showing a mistake, but more of rearrangement.
3. **Step 3**:
- The equation states \(12 + 17x + x^2 = 12 - x^2 + 17x\).
- This indicates the left side has \(x^2\) while the right side has \(-x^2\), suggesting an imbalance created in this step.
To summarize, the error in verification through the commutative property of addition occurs in **Step 3**, where the two sides of the equation are not equal due to having \(x^2\) on the left and \(-x^2\) on the right.
So, the correct response is **Step 3** contains the error.