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The oxygen cycle describes the movement of oxygen within its three main reservoirs.
In summer, monsoon winds bring heavy rainfall from the ocean to the continent.
This animation demonstrates the structure of small, mass-produced circuit boards.
Water turbines convert the kinetic energy of water into electric current.
This animation demonstrates the main sources of soil pollution.
The main sources of water pollution are industry, agriculture and urban areas.
Domesticated animals and crops originate from various parts of the world.
A hot-air balloon is a balloon aircraft which is lifted by hot air.
Regular dice can be used for solving statistical and probability exercises.
To calculate the volume of a tetrahedron we start by calculating the volume of a prism.
Division of space by three intersecting planes in several different arrangements.
The United States entered World War II after the devastating attack by the Japanese navy.
The Crow are Native Americans who inhabited the Yellowstone River valley.
A periodic climate pattern that occurs across the tropical Pacific Ocean every five years.
The bell is a percussion instrument and an idiophone. Many types of bells exist.
Cold and warm fronts are formed where bodies of cold and warm air meet.
Cyclones are large areas of circulating air with clouds and precipitation being formed in its centre.
The piano is one of the most popular instruments in the world. It is a chordophone which produces sounds mechanically.
A string quartet consists of four string players, it appeared in the late 18th century.
The river and marine sailing boats of ancient Egypt were one-masted, oared boats
