The answers are: (a) circle, (b)ellipse, (c) parabola, and (d) hyperbola, as seen in the following four photographs. Comparing the top two pictures (circle and ellipse, respectively), note that the hole is actually the same size and is along the axis of the cone. The three holes in the bottom two pictures (parabola and hyperbola, respectively) have the same spacing and configuration.
Note that the parabola is formed by a section parallel to a line from the tip of the cone along the surface of the cone, whereas the hyperbola is formed by a section parallel to the axis of the cone, as seen below.
You may notice some distortion of the circle and the ellipse in parts (A) and (B) of the figures above. This is due to the way in which your browser may compress the jpegs using different horizontal and vertical attenuation factors. Copying and pasting these pictures onto a non-compressing format should help alleviate this problem.
