Exam 70-483 topic 2 question 139 discussion

You plan to create a list of customers named customers. Each customer will have a name and a key. The name and key will be strings.
You will use the following code to retrieve customers from the list. customers[aKey].toString();
You need to identify which class must be used to declare the customers list. The solution must ensure that each key is unique.
Which class should you identify?