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All the problems in this section are meant to be done with for statement(s)that traverses a string. The functions here all return a value, either an int or a string. None of them should contain a print or an input statement. 1. Write a function that returns the number of occurrences of a lower-case letter 'a' in the argument. 2. Write a function with two arguments, a character, and a string, that returns the number of occurrences of that character in the string. 3. Write a function that returns the number of vowels in a string, where the string is passed as an argument. 4. Write a function that takes a string s as an argument and returns a string in which every vowel in s is replaced by the symbol #. For example, if the argument is the string Kansas City won the Super Bowl this year. then the function will return the string K#ns#s C#ty w#n th# S#p#r B#wl th#s y##r