Choice A is the correct answer. Find the vertices.

1. Intersection 1 ($x=2, y=1$): $(2, 1)$ (Valid: $2+1 \leq 6$)
2. Intersection 2 ($x=2, x+y=6$): $2+y=6 \rightarrow y=4$. Vertex $(2, 4)$.
3. Intersection 3 ($y=1, x+y=6$): $x+1=6 \rightarrow x=5$. Vertex $(5, 1)$.
4. Shape: Three vertices $(2,1), (2,4), (5,1)$ form a right triangle.

?�� Strategic Tip: Sketch the lines to visualize the enclosed region.

Choice B is incorrect because it has 3 sides, not 4. Choice C is incorrect because it has 3 sides. Choice D is incorrect because the region is enclosed by the three lines.