A circle circumscribed about a triangle is one that passes through all three vertices of the triangle. The correct diagram would show a triangle with a circle encompassing it, with the triangle's vertices lying on the circumference of the circle.
Based on your descriptions, the fourth option:
"Triangle upper A upper C upper B is plotted within a circle on a 12 by 9 unit grid. A point inside the triangle is labeled circumcenter."
is the best representation of a circumscribed circle. The circumcenter is the center of the circumscribed circle that passes through the vertices of the triangle.