Final answer:
To look for an existing list, you should select the option to browse, which allows you to view and access lists that have already been created.
Step-by-step explanation:
If you are looking for an existing list, the option you should select is B. browse. When you select the browse option, you are given the ability to view and access lists that have already been created and stored. This is contrary to options such as create list or new list, which are intended for when you want to start a fresh list from scratch. Also, edit recipient list suggests you would be modifying a list, not simply searching for one. Therefore, to look for an existing list, browsing through the available lists is the appropriate action to take.