Final answer:
The correct capitalization in the given sentences is 'My uncle once met the Queen of England', since 'Queen' is a formal title and 'England' is a proper noun.
Step-by-step explanation:
The sentence that shows correct capitalization is: My uncle once met the Queen of England.
According to English capitalization rules, you should capitalize the first word of a sentence and all proper nouns. The word 'uncle' is not capitalized here because it is not being used as part of a specific name. However, 'Queen of England' is a formal title referring to a specific person, and both the title 'Queen' and the identifier 'England' should be capitalized.
It is similar to how you would capitalize Earth when referring to the planet as a proper name, but not when it is used to describe soil or land (the earth).