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A. Incorrect. You can use elimination or substitution to solve the system of equations. You may have thought the value on the right side of the second equation was a solution to the system.

B. Incorrect. You can use elimination or substitution to solve the system of equations. You may have thought the difference between the values on the right side of each equation was a solution, $7-2=5$.

C. Incorrect. You can use elimination or substitution to solve the system of equations. You may have thought the sum of the values on the right side of each equation was a solution to the system, $7+2=9$.

D. Correct. To solve for y, eliminate the x-terms. Start by multiplying both sides of the first equation by 2: $2\left(2x-y\right)=2\left(7\right)\leftrightarrow 4x-2y=14$. Then, add the left and right sides of the two equations: $\left(4x+\left(-4x\right)\right)+\left(\left(-2y\right)+2y\right)=\left(14+2\right)\leftrightarrow 0=16$. Because the resulting equation is false ($0\ne 16$), there is no solution to the system of equations and therefore no such value for $y$.