Complete the following reaction:
`Ar-NH_(2) underset(0-5^(@)C)overset(NaNO_(2),HCl)(to) A overset(CuCN)(to) B`

Explanation

To complete the given reaction, we will follow the steps outlined in the video transcript.

### Step-by-Step Solution:

1. **Identify the Starting Material**:
The starting material is `Ar-NH2`, which represents an aromatic amine (an aromatic ring with an amino group).

2. **Diazotization Reaction**:
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