Early Mizo settlements were often located:

The other options are incorrect because:

• Option b) is incorrect because fertile river valleys are more suitable for agriculture than hilltops. The Mizo people were farmers, and they needed fertile land to grow their crops.
• Option c) is incorrect because dense forests are not suitable for human habitation. The Mizo people needed open land to build their homes and grow their crops.
• Option d) is incorrect because the Mizo people were not a seafaring people. They did not have access to the coast, and they did not engage in trade with other countries.