# If $\overrightarrow a . \overrightarrow a = 0$ and $\overrightarrow a . \overrightarrow b = 0$, then what can be concluded about the vector $\overrightarrow b$?
$\begin{array}{1 1} (A) \overrightarrow b\; is \;collinear \;vector. \\ (B) \overrightarrow b\; is \;unit \;vector. \\ (C) \overrightarrow a\; and \;\overrightarrow b\;are \;equal\; vectors. \\ (D) \overrightarrow b is\; any\; vector. \end{array}$