Final answer:
In the given sentence, 'Jr.' should be capitalized because it is a suffix that is part of a person's full name.
Step-by-step explanation:
The word that needs to be capitalized in the sentence "Michael Blake, jr., is such an accomplished golfer that he won three tournaments in a row." is "Jr." When used as part of a person’s full name, the abbreviation "Jr." for junior, should always be capitalized. Additionally, it should be set off with a comma before it, as seen in the sentence. Therefore, the correct sentence should be: "Michael Blake, Jr., is such an accomplished golfer that he won three tournaments in a row." Proper noun capitalization and the capitalization of titles and suffixes are important rules in English grammar that help with the clarification and proper recognition of names and titles.