If a line makes angle $\alpha,\:\beta,\:\gamma$ with $x-axis,\:y-axis\:and\:\:z-axis$ respectively, then $sin^2\alpha+sin^2\beta+sin^2\gamma=?$

Question

$\begin{array}{1 1} 0 \\ 1 \\ 2 \\ 3 \end{array} $