The aryan migration began its spread into india through the indus river valley because that area

The area had fertile flood plains

Explanation:

The Indus river valley is part of these countries in modern times known as Pakistan and northwest India. the migration of the ARYAN PEOPLE started from Indus river valley because the area was a fertile plain connecting to the near east.

The Aryan people where cattle rearing people and farmers and the needed fertile plains to practice agriculture and also get good grass and water for their cattle hence the civilization/migration started from the Indus river valley for the Aryan people before getting into India

d. the right to establish a one-house legislature

uncle sam would be tossing and turning in his grave : *)