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It is a well-known phenomenon that the sound of an approaching sound source is higher than that of a receding one.
Oil tankers appeared in the late 19th century; today they are among the largest ships.
Wind, as an external force, plays an important role in shaping coastal areas and steppes.
These special dolmens located in present-day Netherlands were built about 5,000 years ago.
Surface tension is the property of a liquid that allows it to obtain the smallest surface area possible.
A presentation of the major administrative units of China.
Practise the English alphabet, build words from letters.
Waterfalls form where a river flows over a steep precipice in its course.
Structures consisting of enormous stone blocks, dating back thousands of years, are monuments of megalithic cultures.
The Hussites mastered the use of war wagons in the 15th century.
Practise the German alphabet and form words from the letters.
Practise the Russian alphabet, build words from letters.
Quetzalcoatlus was one of the largest known flying animals of all time.
A regular square pyramid is a right pyramid with a square base and four triangular faces.
This scene presents the provinces and provincial capitals of the Netherlands.
Today called Dubrovnik, this Croatian city is known for its spectacular architecture and beautiful location.
Many of the most important food crops we consume belong to the family of nightshades.
Organs that detect signals of the environment or of the body and transmit them to the brain as nerve impulses.
This animation helps you learn the basics of healthy eating.
The migration of large human populations began in Ancient times.
This 3D introduces a centipede species widespread in the Mediterranean.
Remarkable civil engineering works to continue the Netherland's centuries-long fight against the sea.