Which point lies on the boundary line of x + y ≥ 3?

Correct answer: (1, 2)

The boundary line of an inequality is obtained by replacing the inequality sign with equality. Thus the boundary of x+y≥3 is the line x+y=3. Test the options in this equation: for (1,2), 1+2=3, so it lies exactly on the boundary. For (1,1), the sum is 2, so it is not on the line. For (3,1), the sum is 4, and for (0,0), the sum is 0; neither equals 3. Notice that the inequality describes a half-plane, while the boundary is only the line separating the accepted and rejected regions. Because the inequality is inclusive, the boundary belongs to the solution region, but the question asks specifically for a point on that line. Therefore option A is the only correct answer.