
The vector field \( \vec{v} \) is given in terms of its components along the \( \hat{i} \), \( \hat{j} \), and \( \hat{k} \) directions. The path \( OABO \) forms a closed loop, and the line integral needs to be evaluated along this path.
By applying the line integral along the closed loop \( OABO \) and performing the necessary calculations, the result is:
\[ \frac{1}{4} (3\pi - 1) \]
Thus, the correct answer is (A).

