The answer is; A
Airports are usually controlled by governments because they are the points of entry and exit into a country and therefore should have enough security and customs. The vulnerability of the industry also from factors such as terrorism and weather requires that the government regulates the industry to protect the country's interests.
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The kind of gas cloud that is most likely to give birth to stars is a cold, dense gas cloud.
Stars are formed in giant molecular clouds, called "star nurseries". These are regions with molecular Hydrogen, Helium, and little amounts of other elements. These are cold and dense regions, and the gas cloud collapses, forming a protostar. The protostar gradually heats, powering nuclear reactions in its center, which increases the temperature even more and giving birth to a star.
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Fusion,melting,vaporization,submlimination are examples of endothermic changes
"Frequency" is a measure of how frequent something is.
Its unit is the "Hertz".
1 Hertz = 1 per second