Answer:
C. One of my ancestors fought at the battle of Gettysburg.
Step-by-step explanation:
Capitalization or the use of capital letters in a sentence or word is used for nouns, especially proper nouns. Moreover, it is also used to start a sentence, with names, months, days, holidays, festivals, etc.
Among the given options, sentence C has an error in the use of capitalization. The "Battle of Gettysburg" is a historical battle fought between the Union and Confederate armies. And thus, the name of the battle is a proper noun. Thus, capital letter should be used when writing the name of the battle.
Thus, the correct way to write the given sentence should be "One of my ancestors fought at the Battle of Gettysburg."
Thus, the correct answer is option C.