Which control structure is used to control the repeated calls of a recursion function? (7) What is the overhead associated with the execution of a recursive function both in terms of memory space and...

Which control structure is used to control the repeated calls of a recursion function? (7)

What is the overhead associated with the execution of a recursive function both in terms of memory space and computer time?  (7)

Write a recursive function, vowels, that returns the number of vowels in a string. Also, write a program to test your function.