Final answer:
The word 'Thanksgiving' should not begin with a capital letter.
Step-by-step explanation:
The fourth Thursday in November is set aside as Thanksgiving Day. Capitalization rules dictate that the days of the week and months of the year should be capitalized, while holidays themselves should not be capitalized unless they are proper nouns. Since Thanksgiving is not a proper noun, the highlighted word 'Thanksgiving' should not begin with a capital letter.
Learn more about Capitalization of holidays