The correct answer is: b) Shell middens.
Shell middens are a type of archaeological site that consists of a deposit of shells, often mixed with other materials such as bones, artifacts, and soil. They are formed when people discard the remains of their meals, such as shellfish, fish, and other marine animals. Shell middens are often found along coastal regions, where they provide evidence of past human habitation.
In Gujarat, shell middens are a common type of Mesolithic site. They are found along the coast of the Arabian Sea, and they provide evidence of a people who lived off of the sea. The middens contain the remains of shellfish, fish, and other marine animals, as well as tools and artifacts made from bone, stone, and shell.
Shell middens are an important source of information about past human cultures. They can provide information about diet, subsistence, technology, and social organization. They can also be used to date archaeological sites and to track changes in human populations over time.
The other options are incorrect because they are not unique to Gujarat or to the Mesolithic period. Cave shelters are found in many parts of the world and were used by people of all ages. Rock art is found in many parts of the world and dates to a variety of time periods. Megalithic tombs are found in many parts of the world and date to the Neolithic period.