Final answer:
The correct word to use is 'their' in the sentence 'Some people march to the beat of their own drummer.'
Step-by-step explanation:
In the sentence, 'Some people march to the beat of their own drummer,' the correct word to use is their. 'Their' is a possessive pronoun that shows ownership. In this case, it indicates that each person marches to their own drummer, meaning they have their own unique way of doing things.
Learn more about Using 'there', 'their', and 'they're' correctly in sentences