Final answer:
The correct label for elevator 2, which moved down 4 feet from the ground level, is a) -4, following the convention that defines upward movement as positive and downward movement as negative.
Step-by-step explanation:
If elevator 1 moved up 8 feet from the ground level and its position is labeled as +8, elevator 2's movement down 4 feet from the ground level would be labeled using a negative sign due to conventional standards that define upward direction as positive and downward direction as negative. Therefore, the correct label for elevator 2's position is -4, marking selection a) -4 as the correct answer.