His actions always have a duality.

My room number is two hundred and five.

He defeated the enemy using a two-sword style.

He holds dual citizenship in America and Japan.

I will turn twenty years old next year.

Carbon dioxide is one of the main causes of global warming.

This factory is emitting a large amount of sulfur dioxide.

I eat lunch at twelve o'clock.

This diode only allows current to flow in one direction.

My younger sister is twenty-one years old.