The celebrations were rounded … with a firework display.

Analyze the question: The sentence needs a phrasal verb that fits "rounded ___ with a firework display." We're looking for the particle that means the celebrations were concluded or finished in a particular way.

Explain the concept: Phrasal verbs with "round" have different meanings depending on the particle:

• round up = to gather together (e.g., round up cattle, or round up suspects), or to raise a number to the nearest whole figure
• round out = to make something complete or well-rounded
• round off = to finish or end something in a satisfying or fitting way
• round down = to lower a number to the nearest whole figure

Solution:

1. The sentence says the celebrations ended with a firework display, so we need a verb meaning "to conclude."
2. "Rounded up" would suggest gathering people or animals, which doesn't fit.
3. "Rounded out" means to complete or fill out something, usually by adding a missing part. It is close but less idiomatic when describing an event ending with a finale.
4. "Rounded down" applies to numbers.
5. "Rounded off with" is the standard idiom for ending an event with a final item: "The evening was rounded off with a song."

off**.

Tip: Think of "round off" like putting the final touch on something, as in "to round off a meal with dessert." Whenever you see "rounded ___ with" and an event is ending, choose off. Remember that "round up" is for gathering and "round down" is for numbers.