The thirteenth day is my birthday.

He drew an equilateral triangle shape.

I cannot know the thoughts buried deep inside her heart.

I can't understand what's in his mind.

He conveyed the schedule of the meeting in a three-line email.

There is a three-way interview at my son's school tomorrow.

Three countries formed an alliance.

His new project meets all three important requirements: funding, personnel, and ideas.

He trains his triceps at the gym every day.

I hit the jackpot with a trifecta.