Explanation:

The successful functioning of the Indian federal system depends not only on the harmonious relations and close cooperation between the Centre and the states but also between the states inter se. Hence, the Constitution makes the following provisions with regard to inter-state comity:
1. Adjudication of inter-state water disputes.
2. Coordination through inter-state councils.
3. Mutual recognition of public acts, records and judicial proceedings.
4. Freedom of inter-state trade, commerce and intercourse.
In addition, the zonal councils have been established by the Parliament (not provided by the Constitution, hence option ‘a’ is the correct answer) to promote inter-state cooperation and coordination.