Determine how many pivots each of the following matrices have.

a$.\left[\begin{array}{cccc}0& 1& 0& 5\\ 0& 0& 1& -9\end{array}\right]$

b$.\left[\begin{array}{ccc}1& 0& -3\\ 0& 0& 0\\ 0& 0& 0\end{array}\right]$

C$.\left[\begin{array}{cccc}1& 0& 0& -3\\ 0& 1& 0& -4\\ 0& 0& 1& -8\end{array}\right]$

d$.\left[\begin{array}{ccc}1& 0& -10\\ 0& 1& 3\\ 0& 0& 0\end{array}\right]$