Solve this following

If a line makes angles $a, \beta$ and $y$ with the $x$-axis, $y$-axis and $z$-axis respectively then $\left(\sin ^{2} a+\sin ^{2} \beta\right.$ $\left.+\sin ^{2} y\right)=?$

A. 1

B. 3

C. 2

D. $\frac{3}{2}$