Which is the bumpiest?

 - rock wall
 - gold ring
 - silk necktie
Bumpy is a property. A bumpy material is covered in lumps and bumps. It is not flat or smooth.
Look at each picture, one at a time. Imagine touching the material shown in each picture.
Of the choices, the rock wall is the bumpiest. If you touch a rock wall, it will feel bumpy and lumpy.