The tilting or folding of horizontal layers must occur a. after the layers have formed b. before the layers have formed c. during the formation of the layers

Option (A)

Explanation:

The layers that creates folding or tilting are found in the sedimentary rocks. These rocks are formed due to the compaction and lithification of sediments. For example, sandstone, shale and mudstone.

This rocks when deposited over one another, it forms layers. These layers are then subjected to folding or tilting due to the compressional stress (tectonic forces).

Before forming the layers, if the rock is subjected to compressional stress, then the sediments will not form layers and there occurs no folding. Whereas it will shatter the rock.

Thus, the correct answer is option (A).