big iron cannon的用法和样例：
- The newspaper today said that a man while digging in his garden found a big iron cannon ball, isn't that weird?
- You are the invincible big iron tongs.
- The apothecary cooked the medicinal mixture in a big iron kettle.
- An iron cannon was actually installed for the purpose of subduing invading forces but it was later dismantled without a shell ever being fired.
- A big iron mine in the district employs mainly outsiders and pollutes a river.