Final answer:
The origin of a river is called its headwaters, and the end where it flows into a larger body of water is known as the mouth. The correct answer is (d) headwaters; mouth is.
Step-by-step explanation:
The area of the origin of a river is its headwaters, and the mouth is the end of the river. The correct answer to the multiple-choice question is (d) headwaters; mouth is. Rivers and streams begin at a point of origin referred to as source water or headwaters, which is usually cold, clear, and with low nutrients. The channel here is narrower and the current is often faster due to the higher elevation and steeper grades. As the river flows, it carries water to its mouth, where it empties into a larger body of water such as a lake or ocean. The mouth of a river is typically found at a lower elevation than the headwaters.