One way to add a correctly spelled word to the custom dictionary is to tap or click the ____ button in the Spelling and Grammar dialog box.

A) Add to Dictionary
B) New Entry
C) Add to Custom
D) Custom Entry

The "Add to Dictionary" button is specifically designed to add words to the custom dictionary, allowing the user to include correctly spelled words that may not be recognized by the program's built-in dictionary. This choice is the best option as it is straightforward and directly addresses the task of adding a word to the custom dictionary.