What he did was an irretrievable mistake.

He tidied up the room quickly.

Keiko is my best friend.

His behavior was not suitable for his position.

He learned the style of the painting to imitate the ancient artist.

He claimed that the terrorist attack was a false flag operation.

It's a beautiful night with the moon.

There is a small mound in the park.

There is a new desk in my room.

There are many books on my desk.