Write a function in Python 3.6 that receievs 2 strings as parameters. The first parameter is a sentence, while the second string will contain any combination of characters (letters, numbers, space, special characters, etc.). Your code should find which of the given characters in the second parameter appears most frequently in the sentence string. Case should not be ignored, so for example, A and a should be considered two different characters. If no characters appear, an empty string should be returned. If there is a tie between multiple letters, return the character that appears first.