The dialogue with him is always fun.

This object is the focus of my research.

He is good at writing antithetical couplets.

This is absolutely without a doubt.

He learned how to operate a howitzer.

He pointed the muzzle of the gun at the enemy.

He fired a cannonball.

When he hears the sound of the organ gun, he recalls the horrors of war.

He learned how to operate an anti-aircraft gun.

He learned how to operate a cannon.