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.

Kenjiro is my best friend.

Keijiro is my best friend.

He was working abroad for twelve months.

He chose to serve a second master by working hard.