Let

\[
\begin{aligned}
& \dot{x}=\left[\begin{array}{ll}
1 & 2 \\
0 & 1
\end{array}ight] x+\left[\begin{array}{l}
0 \\
1
\end{array}ight] u \\
& y=\left[\begin{array}{ll}
b & 0
\end{array}ight] x
\end{aligned}
\]

where \(b\) is an unknown constant.

This system is
(a) observable for all values of \(b\)
(b) unobservable for all values of \(b\)
(c) observable for all non-zero values of \(b\)
(d) unobservable for all non-zero values of \(b\)