Explanation:

Recommendations of different committees:
Ashok Mehta Committee: The three-tier system of panchayati raj should be replaced by the two-tier system, that is, zila parishad at the district level, and below it, the mandal panchayat consisting of a group of villages with a total population of 15,000 to 20,000.
Balwant Rai Mehta Committee: Establishment of a three-tier panchayati raj system—gram panchayat at the village level, panchayat samiti at the block level and zila parishad at the district level. These tiers should be organically linked through a device of indirect elections.