Write a function to replace at least four different phrases (of two or three words) with established acronyms (e.g., replace "BY THE WAY" with "BTW") of your choosing. This function must take only the string to be modified as an argument and must return the string with the replacements. You may not use any built-in find, replace, encode, or translate functions, but you may write your own version of these functions if you wish, and you may use the indexing operator (i.e., the square brackets), the slicing operator (i.e, the colon), the "in" operator, and the lenO function