The correct option is (b).
Explanation
Plains are broad, flat, or gently rolling areas of land. They are one of the major landforms on Earth and are primarily associated with lowlands, though their formation involves various geomorphic agents.Statement 1 is Incorrect: Most plains are not formed by wind erosion. The vast majority of plains, especially the most fertile and densely populated ones, are formed by the action of rivers and their tributaries (alluvial plains). While wind can create landforms (such as loess plains via deposition or pediplains via erosion), it is not the primary agent for the formation of "most" plains globally.
Statement 2 is Correct: This describes the primary mechanism of alluvial plain formation. Rivers flowing from mountains erode the steep slopes and carry eroded material (load) such as stones, sand, and silt. As the river reaches gentler slopes or valleys, its velocity decreases, leading to the deposition of this load. Over time, these deposits accumulate to form extensive plains.
Statement 3 is Incorrect: Plains are generally low-lying landforms. Most plains are situated not more than 200 metres above mean sea level. While there are exceptions (such as high-altitude plains), the general definition distinguishes plains from plateaus and mountains by their relatively lower elevation.
Key Takeaway: The most common plains are depositional landforms created by rivers carrying alluvium from mountains to low-lying areas, typically found at elevations below 200 metres.