Solution:The following statements are correct in the context of the geomorphic cycles of Davis and Penck: Davis considered the cycle of erosion by the fluvial process as the 'Normal Cycle of Erosion'. Davis used the concept of slope decline.
In the second sub-stage of the phase of synchronous landscape development in the Penck model, there is no increase in absolute height, nor is there an increase in relative relief, because the rate of summit lowering and uplift are equal. Davis did not use the concept of Base Level proposed by Gilbert and graded streams propounded by Powell to apply the evolutionary paradigm.
Powell propounded his concept on the 'Base Level' in 1875 AD. According to Powell, the sea level represents the main base level, below which sub-aerial erosion cannot occur. Mr. Gilbert propounded a theory based on the relationship between river velocity and river carrying power, which is called Gilbert's Law of Sixth Power. According to this theory, the transporting power of a river is proportional to the sixth power of the river's velocity.
Gilbert used the scientific method in the analysis of landforms and processes, which emphasizes quantity over quality. He used the thermodynamic model in the analysis of geological processes. Davis first propounded a genuine General Theory' related to the development of landforms.
His geomorphic theory is a collection of several concepts. The three main ones are: (1) The complete cycle of stream life, (2) The geographical cycle, (3) Slope development. Davis observed the cyclical method in the development of landforms in a historical context. He stated that the construction and development of landforms are influenced by structure, process, and time.
Thus, option (e) is correct.