Choice D is correct. A system of two linear equations in two variables, and , has no solution if the lines represented by the equations in the xy-plane are distinct and parallel. The graphs of two lines in the xy-plane represented by equations in the form , where , , and are constants, are parallel if the coefficients for and in one equation are proportional to the corresponding coefficients in the other equation. The first equation in the given system can be written in the form by subtracting from both sides of the equation to yield . The second equation in the given system can be written in the form by subtracting from both sides of the equation to yield . The coefficient of in this second equation, , is times the coefficient of in the first equation, . For the lines to be parallel, the coefficient of in the second equation, , must also be times the coefficient of in the first equation, . Thus, , or . Therefore, if the given system has no solution, the value of is .
Choice A is incorrect. If the value of is , then the given system would have one solution, rather than no solution.
Choice B is incorrect. If the value of is , then the given system would have one solution, rather than no solution.
Choice C is incorrect. If the value of is , then the given system would have one solution, rather than no solution.