5. Which of the following is not a system of linear equations in two variables? *
A. \( \{ 4 x - y = 5,3 x + y = 7 \)
B. \( \{ x - y = 9,2 x + y ^ { \wedge } 2 = 7 \)
C. \( \{ x - y = - 5 , y = 7 x \)
D. \( \{ x + y = 3 , y + 7 x = 1\)
5. Which of the following is not a system of linear equations in two variables? *
A. \( \{ 4 x - y = 5,3 x + y = 7 \)
B. \( \{ x - y = 9,2 x + y ^ { \wedge } 2 = 7 \)
C. \( \{ x - y = - 5 , y = 7 x \)
D. \( \{ x + y = 3 , y + 7 x = 1\)
B