Answer:
A. He drew a horizon line to show where the sky and earth appear to meet.
B. He used a vanishing point to draw objects that run horizontally across the painting.
D. He used orthogonal lines to draw the sides of objects that run towards the vanishing point
Step-by-step explanation:
A painting with one-point perspective contains only one vanishing point on the horizon line, which in the case of da Vinci's The Last Supper is the line where the sky and earth meet. Thanks to this perspective, things shown in the painting appear to get smaller as they get further away. Objects feel three-dimensional, despite being shown on a two-dimensional surface.
The picture below shows how da Vinci use one-point perspective. We can see how he used a vanishing point to draw objects that run horizontally across the painting, as well as the orthogonal lines to draw the sides of objects that run towards the vanishing point.