He is researching about a new energy source.

It is important to understand the importance of health.

His explanation was impossible to understand.

Please use the emergency stairs in case of a fire.

Due to the earthquake, the city declared a state of emergency.

This is a historic building.

He is a famous historian and has written many history books.

He is majoring in history at university.

He is trying to hide his embarrassing past.

He recognizes the importance of oral history.