1. The problem asks for the angle between two parallel vectors. 2. Recall that parallel vectors point in the same or exactly opposite directions. 3. The angle $\theta$ between two vectors $\mathbf{a}$ and $\mathbf{b}$ is given by the formula: $$\cos(\theta) = \frac{\mathbf{a} \cdot \mathbf{b}}{|\mathbf{a}||\mathbf{b}|}$$ 4. For parallel vectors, the angle $\theta$ is either $0^\circ$ (if they point in the same direction) or $180^\circ$ (if they point in opposite directions). 5. Among the given options, $0^\circ$ is the correct angle between two parallel vectors. **Final answer:** A) $0^\circ$