How can I change a string.

[buran]

well this breaks the example both in terms of example input and expected output.
It breaks the example input as I understood it - a word in words list is concatenated to previous word, i.e. my understandig was the input would be When parents goWhat do they listen toWhyHow
It breaks the expected output as I understood it - a word in list is preceded by dot and space, i.e. making a complete sentence.
When parents go. What do they listen to. Why. How

All that said - define explicit rules how the input string will look like and what the expected output should be and then a more complex parser should be created