Determine how many pivots each of the following matrices have.

1. Choose One Pivot Two Pivots Three Pivots Four Pivots $\left[\begin{array}{ccc} 1 &0 &3\cr 0 &0 &0\cr 0 &0 &0 \end{array}\right]$
   
   
2. Choose One Pivot Two Pivots Three Pivots Four Pivots $\left[\begin{array}{cccc} 1 &0 &4 &9\cr 0 &1 &-9 &8\cr 0 &0 &0 &0\cr 0 &0 &0 &0 \end{array}\right]$
   
   
3. Choose One Pivot Two Pivots Three Pivots Four Pivots $\left[\begin{array}{ccccc} 1 &0 &0 &0 &7\cr 0 &1 &0 &0 &-9\cr 0 &0 &1 &0 &-3\cr 0 &0 &0 &1 &10 \end{array}\right]$
   
   
4. Choose One Pivot Two Pivots Three Pivots Four Pivots $\left[\begin{array}{cccc} 0 &1 &0 &5\cr 0 &0 &1 &9 \end{array}\right]$