The reduced row-echelon forms of the augmented matrices of four systems are given below. How many solutions does each system have?

1. $\left\lbrack \begin{array}{rrr|r} 1 & 0 & 0 & 7 \\ 0 & 0 & 1 & -15 \end{array} \right\rbrack$
   
   A. Infinitely many solutions
   B. Unique solution
   C. No solutions
   D. None of the above
   
   
   
2. $\left\lbrack \begin{array}{rrr|r} 1 & 0 & 16 & 0 \\ 0 & 1 & 19 & 0 \\ 0 & 0 & 0 & 1 \end{array} \right\rbrack$
   
   A. No solutions
   B. Infinitely many solutions
   C. Unique solution
   D. None of the above
   
   
   
3. $\left\lbrack \begin{array}{rrr|r} 1 & 0 & -12 & 0 \\ 0 & 1 & 0 & 0 \\ 0 & 0 & 0 & 1 \\ 0 & 0 & 0 & 0 \end{array} \right\rbrack$
   
   A. Unique solution
   B. No solutions
   C. Infinitely many solutions
   D. None of the above
   
   
   
4. $\left\lbrack \begin{array}{rr|r} 1 & 0 & 14 \\ 0 & 1 & 8 \\ 0 & 0 & 0 \end{array} \right\rbrack$
   
   A. Unique solution
   B. No solutions
   C. Infinitely many solutions
   D. None of the above