Imagine that you wanted to write a program that asks the user to enter in 5 grade values. The user may or may not enter valid grades, and you want to ensure that you obtain 5 valid values from the user. Which nested loop structure would you use? A. A "for" loop inside of a "while" loop
B. A "while" loop inside of a "for" loop
C. None of the above
D. Either a or b would work

B. A "while" loop inside of a "for" loop

Explanation:

To enter 5 grade values, a for loop can be used to specify the number of grade values to be entered by the user, in other to ensure the validity of the grade values entered by the user, the while loop will be used inside the for loop such that the inputted values will only be accepted when the user enters a valid grade.

Code structure :

For a in range(0, 5) :

grade = input()

while grade (enter condition)

This is just the code structure and this will work for the problem stated.