The correct answer is: a) Large stone structures.
Megaliths are large stones that have been erected by humans. They can be found in many parts of the world, including Mizoram. Megaliths are often used for religious or ceremonial purposes. They can also be used as tombs or markers for important people.
Option b) is incorrect because natural rock formations are not created by humans. Option c) is incorrect because recent religious monuments are not typically made of stone. Option d) is incorrect because irrigation channels are not made of stone.
Megaliths are a fascinating part of human history. They can provide us with insights into the beliefs and practices of ancient peoples.