It is commonly known that in a typical English text, some letters occur more frequently than others. For example, in a long text, approximately 12.31% of the letters will be 'e'. Your friend from the linguistics department has asked you to help him find the most common letters in a given text.
The text is given to you in the String text. Return the letter that occurs most frequently in text. If there are multiple letters that occur most frequently, return all of them in alphabetical order. See examples for further clarification.