The 91st Constitution Amendment Act is the correct answer.

Option 1 is accurate because the 91st amendment, enacted in 2003, imposes a limit on the size of the Councils of Ministers at both the Centre and State level. According to this amendment, the size must not exceed 15% of the total number of members in the Lok Sabha and the Legislative Assembly of that State, respectively.

Option 2, the 93rd amendment, is incorrect because it pertained to education, providing for reservations for "socially and educationally backward classes", Scheduled Castes and Scheduled Tribes in private unaided schools.

Option 3, the 95th amendment, is incorrect as its main purpose was to extend the reservation of seats for Scheduled Castes and Scheduled Tribes in the Lok Sabha and State Assemblies.

Option 4, the 97th amendment, is also incorrect as this amendment deals with matters related to co-operatives. It added a new Part IXB in the Indian Constitution related to the co-operative societies.

Thus, only the 91st Amendment Act has a regulation that directly pertains to the size of Councils of Ministers in the context described.