Final answer:
In the provided options, only the option (d) 1x₁+1x₂ could represent the objective function, which is the equation used to maximize or minimize in a linear program, because it lacks an inequality or equality sign.
Step-by-step explanation:
In a linear program, the objective function is usually an equation that represents a quantity to be maximized or minimized, subject to a set of constraints. The options provided: (a), (b), and (c) are constraints because they contain inequalities. These are the restrictions that the values of x₁ and x₂ must satisfy. Option (d), written as 1x₁+1x₂, does not have an inequality or equality sign and could represent the objective function, indicating that the sum of x₁ and x₂ is to be optimized (either maximized or minimized) in this linear program.