Which assertion is true about mailing fireworks?

Mailing fireworks is strictly prohibited due to safety concerns and regulations in place for explosive materials. Fireworks are classified as hazardous materials, and the potential risks associated with their shipping—such as accidental ignition and explosion—make mailing them highly dangerous. This prohibition is enforced by various transportation authorities and is designed to protect public safety and prevent accidents during shipping processes.

The other statements either suggest allowances or conditions that don't align with the strict regulations in place. For example, the idea that mailing fireworks could require multiple permits does not hold as there are generally no permits that would permit the mailing of fireworks. Likewise, suggesting that fireworks could be mailed under a specific weight misrepresents the outright ban on their shipment. Since the regulations are clear and stringent, the assertion that mailing fireworks is strictly prohibited stands as the only accurate statement.