A long, straight wire carries a constant electric current \(I\). Ampère's law, \(\oint \vec{B} \cdot d\vec{\ell} = \mu_0 I_{\text{enc}}\), is used to calculate the magnitude of the magnetic field at a distance \(r\) from the center of the wire. Which of the following correctly explains why a circular Amperian loop centered on the wire is chosen and correctly interprets the meaning of \(I_{\text{enc}}\)?