When John was asked to memorize 15 alphabets in a particular order, he organized them into groups of three letters each and memorized them in the given order. In this scenario, John has used the tactic of

Chunking

Explanation:

Chunking is a term referring to the process of taking individual pieces of information (chunks) and grouping them into larger units. By grouping each piece into a large whole, you can improve the amount of information you can remember. So that's what John did by grouping them into 3 letters each.

all cities have a governor

all cities are in states or provnies then country

all cities have people

difference

some are rich

some are poor

some are average