A geologist would study dendritic patterns to infer that running water was the "primary agent" to have formed the landscape. Dendritic drainage patterns occur when streams follow the path of least resistance, carving through pre-existing valleys and other landscape features.In dendritic patterns, a main river or stream channel branches out into a network of smaller streams that resemble the branches of a tree or the veins in a leaf. This drainage pattern is created when a river flows over relatively uniform terrain consisting of permeable rocks, such as sandstone or shale, and creates smaller streams that flow into the main channel.Thus, a geologist would use dendritic patterns to infer that running water was the "primary agent" that formed the landscape. Answer: b. the dendritic patterns