What is the ultimate base level of a stream? a large lake the ocean a resistant layer of rock a larger stream

The **ultimate base level** of a stream is **the ocean**. ### Explanation: - **Base Level**: In geomorphology, the base level is the lowest point to which a stream can erode its bed. It serves as a reference point for the stream's ability to erode and transport sediment. - **Ultimate Base Level**: This refers to the most fundamental base level, which is typically sea level. All other base levels (like lakes or larger streams) are considered *local* base levels that ultimately drain into the sea. - **Other Options**: - **A large lake** can act as a base level for streams flowing into it, but it is not the ultimate base level unless the lake itself drains into the ocean. - **A resistant layer of rock** can create a temporary or local base level by preventing further erosion at that point, but it does not represent the ultimate base level. - **A larger stream** can serve as a base level for smaller tributaries, but the ultimate base level is still the ocean where all streams ultimately drain. **Correct Answer:** the ocean