If you want to omit a grammar suggestion without changing it, what should you select?

Selecting "IGNORE ONCE" is the correct action to take when you want to omit a single grammar suggestion without making any changes to it. This option allows you to acknowledge the suggestion but decide not to apply it at that moment, letting the text remain as it is. Choosing this option effectively tells the grammar checking tool to disregard the highlighted issue just for that specific instance.

In contrast, other options involve different actions. For example, adding a suggestion to the dictionary would mean that you consider the suggestion correct in the future, whereas "IGNORE ALL" would dismiss all instances of that particular suggestion throughout the document, which may not be what you want if there are other occurrences that you might wish to address. Closing the grammar pane doesn't directly engage with any specific suggestion and simply removes the feedback window, which does not help in taking any action on the suggestion itself.