The correct answer is: b) Stone tools.
Evidence of prehistoric human habitation in Sikkim has been found primarily in the form of stone tools. These tools have been found in various parts of the state, including the Teesta Valley, the Rangit Valley, and the Singalila Range. The tools are made from a variety of materials, including chert, quartz, and sandstone. They are of various shapes and sizes, and they are thought to have been used for a variety of purposes, such as hunting, gathering, and woodworking.
The discovery of these tools provides evidence that humans have been living in Sikkim for at least several thousand years. It also provides insights into the lives of these early inhabitants, their hunting and gathering practices, and their tool-making skills.
The other options are incorrect because:
- Cave paintings are not common in Sikkim.
- Pottery shards have been found in Sikkim, but they are not as common as stone tools.
- Ruins of settlements have been found in Sikkim, but they are not as old as the stone tools.