The correct answer is: a) Controlling trade routes.
Mizo chiefs controlled trade routes that passed through their territory, and they collected tolls from merchants who used these routes. This gave them a significant source of power and revenue.
Option b) is incorrect because Mizo chiefs did not collect taxes on land. Land was owned by individual families, and the chiefs did not have the authority to tax it.
Option c) is incorrect because Mizo chiefs did not receive tribute from neighboring states. The Mizo people were a fiercely independent people, and they did not pay tribute to any other state.
Option d) is incorrect because Mizo chiefs did not have any manufacturing industries. The Mizo people were a subsistence agricultural people, and they did not produce any manufactured goods.