Final answer:
The term described as the beginning of a river is c) "Source". It is the point where a river starts and is characterized by cold, clear water with a faster current due to a narrow channel.
Step-by-step explanation:
The term that is described as the beginning of a river is c) "Source". The source of a river, or headwater, is the point of origin where the river begins its flow. Typically, the source water is characterized as being cold, having low nutrient levels, and being clear. The stream channel at this point is also often narrower compared to other parts along the river's length, leading to a faster current.It is important not to confuse this with other terms related to rivers such as the mouth, delta, or estuary. The mouth of a river is where it flows into another body of water, such as a lake or an ocean. A delta is a landform created at the mouth of a river where it deposits sediment, and an estuary is a partially enclosed coastal body of water where freshwater from rivers and streams meets and mixes with salt ocean water. Although these features are associated with rivers, they are not where rivers begin.In conclusion, the source of a river is its origin, marking the start of its journey to larger bodies of water, contrasting with other terms like mouth or estuary that describe where rivers end or interact with other environments.