Lacustrine plains are formed

Lacustrine plains are formed on the bed of an old lake. A lake is a body of water surrounded by land, and over time, sediments can accumulate at the bottom of the lake. When the lake dries up or drains, the sedimentary deposits left behind form a flat plain. These plains can be found in various parts of the world, and they can be quite extensive. The sedimentary deposits can include a range of materials, such as clay, sand, and silt, which can have economic value. In addition to their economic importance, lacustrine plains can also be ecologically valuable, providing habitat for a variety of plants and animals. Therefore, the correct option is: on the bed of an old lake.