Click the Ignore All button the first time the word is flagged in each document.
Explanation:
Click the Ignore All button the first time the word is flagged in each document – This option best suit since the word is expected to be used frequently, it should ignore in all occurrences of the document.
Whereas other shouldn’t add because this task is permanent and we don’t want it to happen once again in another word document. This is a time consuming process and will reduce the productivity.
Click the Change All button the first time the word is flagged in each document option should be used only when we replace all occurrences .