B. $\left\{ \begin{array}{r@{}r@{}l} y_1 & = & 0 \cr y_2 & = & 7 x_2 \end{array} \right .$

C. $\left\{ \begin{array}{r@{}r@{}l} y_1 & = & - 8 x_1 \cr y_2 & = & 2 x_1 \cr y_3 & = & 9 x_1 \end{array} \right .$

D. $\left\{ \begin{array}{r@{}r@{}l} y_1 & = & 4 x_2 \cr y_2 & = & - 9 x_3 \cr y_3 & = & - 10 x_1 \end{array} \right .$

E. $\left\{ \begin{array}{r@{}r@{}l} y_1 & = & 10 x_1 \cr y_2 & = & 6 \cr \end{array} \right .$

F. $\left\{ \begin{array}{r@{}r@{}l} y_1 & = & 3 \cr y_2 & = & 7 \cr y_3 & = & 4 \cr \end{array} \right .$