This building is a symbolic landmark of our town.

This work of art is considered to be very valuable.

He is a famous sculptor.

This invention brought about an epoch-making advancement in science and technology.

A new school term is starting.

What is the half-life of this substance?

"Once in a lifetime" means to cherish the encounter that happens only once in one's lifetime.

He missed a once-in-a-lifetime opportunity.

The story of the time of creation is mysterious and interesting.

His dog is currently in its sexually active period.