The correct answer is option (4) (C), (B), (A), (D).

Here is the reason behind the correct sequence of events:

(C) In mountainous regions there are a large number of perennial streams: Mountainous regions typically have a high number of perennial streams due to the continuous flow of water, making them suitable for setting up mini hydel plants.

(B) The energy of the perennial streams can be used to move small turbines: The continuous flow of water in perennial streams possesses kinetic energy that can be harnessed to rotate small turbines.

(A) The turbines generate electricity: The movement of the turbines due to the flow of water generates electricity through the process of electromechanical energy conversion.

(D) This electricity can be used to meet local demands: The electricity generated by the mini hydel plants can be utilized to fulfill the energy requirements of the local communities in the surrounding areas.

This arrangement logically represents the sequence of events in the context of the establishment and functioning of mini hydel plants in mountainous regions.