Final answer:
The black line is shorter than the gray line.
Step-by-step explanation:
According to the clues, we know that:
- A black line is shorter than a white line
- The white line is shorter than a gray line
From these clues, we can conclude that the black line is shorter than the gray line. This is because the white line is shorter than the gray line, and the black line is shorter than the white line. Therefore, the black line is indeed shorter than the gray line.