If $|\overrightarrow{a+b}|=|\overrightarrow{a-b}|$ then

Question

$$\begin{array} {1 1}(1)\overrightarrow{a} \; is\; parallel \;to\; \overrightarrow{b}&(2)\overrightarrow{a} \; is\; perpendicular\; to\; \overrightarrow{b}\\(3)|\overrightarrow{a}|=|\overrightarrow{b}|&(4)\overrightarrow{a}\; and \; \overrightarrow{b}\; are \;unit \;vectors\end{array}$$