Answer
The strings that conform to the structure Chacha consist of one or more of the following substrings:
forward backward cha cha cha
backward forward cha cha cha
swing right cha cha cha
swing left cha cha cha
Work Step by Step
The strings that conform to the structure Chacha consist of one or more of the following substrings:
forward backward cha cha cha
backward forward cha cha cha
swing right cha cha cha
swing left cha cha cha