Final answer:
The best command to resolve David Trueheart's name being flagged as misspelled is 'Add to dictionary', as it will prevent future spellcheck flags without altering the correct spelling.
Step-by-step explanation:
David Trueheart's last name is being flagged as misspelled in his presentation slides. To resolve this issue, since it is a proper noun and spelled correctly, the most appropriate command to use would be Add to dictionary. This option will teach the spellcheck program that "Trueheart" is indeed spelled correctly and should not be marked as an error in the future. The other options, such as Ignore, will only skip the word once or for the session, while Change would replace it with a different word. Meanwhile, AutoCorrect could be used to automatically replace a commonly misspelled word with the correct spelling, which is not necessary in this case. After adding his last name to the dictionary, David will not encounter this problem again in his current and future presentations.