Final answer:
The most significant agent of erosion is water, which not only carves and shapes the landscape but also affects ecosystems by transporting sediments and minerals essential for aquatic life.
Step-by-step explanation:
The most significant agent of erosion is b. water. Water is a key geographic factor and constitutes a significant part of the hydrosphere. It shapes the Earth's surface through continuous processes over time. Rivers, for example, erode rocks in their upper course and transport sediments to be deposited in wider, lower areas like flood plains. On a larger scale, water has been responsible for carving out river valleys in mountains and forming features on coastlines such as cliffs and caves.
Furthermore, these erosion activities increase the levels of dissolved minerals in bodies of water, which are vital for aquatic life. While other factors like wind, gravity, and human activity also cause erosion, the impact of water is the most extensive and constantly reshaping landscapes, ranging from the slow grinding down of rocks to swift changes brought on by events like floods.