Final answer:
Wide streams and valleys are characterized by features such as natural levees and broad floodplains, which are indicative of the lower course of a river with a slower water flow.
Step-by-step explanation:
The features that characterize wide streams and valleys include b. natural levees; broad floodplains. These features are typically found in the lower course of a river, where the water flow is generally slower and the river has a wider channel. Natural levees are formed by sediments deposited during floods, while a broad floodplain is a flat area that extends from the banks of the river and is periodically flooded. This contributes to the valley's width and can support various ecosystems.