答案：C

解析：

The fact that function f of x less than or equal to u for all values of x means that the point P (t,u) is the maximum of the quadratic function f, so P (t,u) must be the vertex of the parabola. The parabola intersects the x-axis at the points (1,0) and (4,0), so t must be halfway between 1 and 4. Therefore, t = 1 + ((4-1)/2) = 2.5. Of the choices, the only one with x-coordinate equal to 2.5 is (2.5,3). Therefore, (2.5,3) could be the coordinates of point P.