How many times have you sung that song?

What floor is the library on?

How many times have you been to Japan?

Index fossils are an important clue to indicate a specific geological era.

By chance, he met my old friend.

In the early morning, he brewed coffee and started his day.

He completed the project in a week.

I'm always busy during the daytime, and I only have time to rest at night.

He had been working overseas for an extended period of time.

The theory of spacetime is an important part of physics.