He researched his family tree to go back through his ancestors' history.

The culture of the Korean Peninsula is very unique, and its history dates back to ancient times.

We often have picnics by the river on weekends.

We often have picnics by the river on weekends.

We have a picnic by the river every weekend.

Salmon return to their spawning grounds by going upstream.

Salmons make a great effort to go upstream the river.

The Adige is the second longest river in Italy.

The Congo River is the largest river in Africa.

The Danube is one of the longest rivers in Europe.