Which of the following loops is best implemented with a while loop?

Group of answer choices

Looping through the characters in a string, and displaying 'yes' if it contains a vowel.

Checking to see if a list of integers contains the value $12.$

Counting how many keys in a dictionary start with the letter $\text{'}$A$\text{'}.$

Asking the user to enter positive integers, exiting by entering $-1.$