Correct Option: A

The correct sequence of plants in a hydrosere is Volvox, Hydrilla, Pistia, Scirpus, Lanatana and Oak. A hydrosere is a plant succession which occurs in a fresh water lake. In time, an area of open fresh water such as a lake will naturally dry out, ultimately becoming woodland. During this change, a range of different landtypes such as swamp and marsh will succeed each other. The succession from open water to climax woodland is likely to take at least two hundred years.