OG详解-OG1 数学1 Q8

Choice D is correct. Since x represents the number of 1-point questions and y represents the number of 3-point questions, the assignment is worth a total of 1•x + 3•y , or x + 3 y , points. Since the assignment is worth 70 points, the equation x +3y = 70 represents this situation.
Choice A is incorrect and may result from conceptual errors. Choice B is incorrect and may result from conceptual errors. Choice C is incorrect and may result from conceptual errors.