If $\overrightarrow{a}$ and $\overrightarrow{b}$ are two unit vectors and $\theta $is the angle between them, then $(\overrightarrow{a}+\overrightarrow{b})$ is a unit vector if

Question

\[\begin{array}{1 1}(1)\theta =\large\frac{\pi}{3}& (2)\theta =\large\frac{\pi}{4}\\ (3)\theta=\large\frac{\pi}{2}& (4)\theta=\large\frac{2\pi}{3}\end{array}\]