What type of stress causes rocks to deform and change shape?

The most appropriate choice in this context is strain, as it refers to the actual deformation or change in shape that occurs in rocks as a result of applied stress. Strain quantifies how much a material deforms in response to stress, which can manifest through changes in length, volume, or shape of the rocks.

On the other hand, compression, tension, and shear are types of stress that can cause deformation in rocks. Compression refers to stress that results in the squeezing of rocks, while tension refers to stress that causes stretching. Shear involves forces that cause one part of a material to slide past another. While all these stresses can lead to deformation, it is strain that directly describes the change in shape resulting from these stresses. Thus, the appropriate answer focuses on the concept of strain indicating the specific changes observed in the material.