Choose the correct answer if θ is the angle between two vectors $\overrightarrow a$ and $\overrightarrow b$, then $\overrightarrow a \: . \: \overrightarrow b\ \: \geq 0$ only when

Question

$$\begin{array} (A)\; 0 < \theta < \frac{\pi}{2} \quad & (B)\; 0 \: \leq\: \theta\: \leq \: \frac{\pi}{2} \quad \\(C)\; 0 < \theta < \pi \quad &(D)\; 0\: \leq\: \theta\: \leq \: \pi \end{array}$$