Careful tooth brushing is an important part of oral hygiene.
The most important weapons of medieval Arab warriors were the bow and the sword.
Observatories are often built at high elevations to minimise the effects of atmospheric turbulence
The Aztec Empire was a despotic, militaristic state ruled by the tlatoani.
The ruler of the vast Mongol Empire was the Khan.
The river and marine sailing boats of ancient Egypt were one-masted, oared boats
Airports provide infrastructure and services necessary for aviation.
Common ciliated eucaryotic unicellular organisms widespread in freshwaters.
The Incas´ rudimentary weapons were inadequate in their struggle against the Spanish Conquistadors.
Honeybees produce a sweet and nutritious substance, honey.
One of the positive influences of the Ottoman invasion of Europe was the construction of baths.
One of the most important monocot crops.
Viking leaders were elected from tribe members by the right of blood or an act of bravery.
The phosphorus cycle describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere.
A fjord is a long, narrow inlet with steep sides, created in a valley carved by glacial activity.
The last Ice Age ended about 13 thousand years ago.
A geyser is a spring characterised by intermittent discharge of water and steam.
System that satisfies consumers’ demands of water supply, wastewater disposal, electricity, heat and gas supply and telecommunication.
Chlorophyll is a photosensitive green pigment found in plants; it absorbs light energy, thus plays a vital role in photosynthesis.
The migration of large human populations began in Ancient times.