What makes up a river system?

Correct answer: Main river and its tributaries

The direct answer is A: a main river and its tributaries. A river system is the connected network formed by the main river, smaller tributaries, and the channels through which their water flows. The reasoning is: rain or melting snow produces runoff; small streams collect and join; these streams become tributaries; tributaries flow into a larger main river; the combined network is called a river system. Option A is correct because it includes the central river and the smaller rivers that feed it. Option B is wrong because sea waves are coastal processes and are not the components of a river system. Option C is wrong because desert sand may be carried by wind or water but does not form a river network. Option D is wrong because mountain peaks may be sources or boundaries, but peaks alone are not a river system. A drainage basin is the area drained by a river and its tributaries, while the river system refers to the connected channels themselves. Remember the key word “tributary”: tributaries join the main river to form the system.