This is one of the questions I'm trying to solve. The answers are below but I'm unsure of which one is the right one. If anyone could explain I'd really appreciate it.

A block of mass m is attached to a horizontal spring and rests on a flat, smooth surface as seen in the figure. The block can be pushed in the negative x-direction to compress the spring or pulled in the positive x-direction to stretch the spring. Where along the x-axis does the block have to be for the spring to have zero potential energy?

• The spring has zero potential energy when the block is at x = -x_max, where the spring is compressed to its maximum value.
• The spring has zero potential energy when the block is at x = +x_max, where the spring is stretched to its maximum value.
• The spring has zero potential energy when the block is at x = 0, where the spring is neither stretched nor compressed.
• The spring has zero potential energy when the block is at either x = ±x_max, where the spring is stretched/compressed to its maximum value.
• The spring always has non-zero potential energy no matter where the block is located.