<human>: Objective: How do you make sure a shelf is straight before hanging it?

Which of the following solutions is more sound in terms of naive physics reasoning?

OPTIONS:
- Make a mark where you would like to place the fasteners for the shelf. Hold your shelf up in that area and place a level on it.
- Make a mark where you would like to place the fasteners for the shelf. Hold your shelf upside down in that area and place a level on it.
<bot>: Make a mark where you would like to place the fasteners for the shelf. Hold your shelf up in that area and place a level on it.