A subquery is a query(expressed as a SELECT statement) that is located inside another query. The first SQL statement is known as the outer query, the second is known as the inner query or subquery. The inner query or subquery is normally executed first. the output of the inner query is used as the input for the outer query. A subquery is normally expressed inside parenthesis and can return zero, one or more rows and each row can have one or more columns.
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Seismic waves, the waves of energy that travel through the Earth as a result of an earthquake can tell us a lot about the internal structure of the Earth because these waves travel at different speeds in different materials. There are two types of waves that travel through the Earth: p-waves and s-waves.
P- waves are faster and they can travel through both solids and liquids. S-waves are slower and cannot travel through liquids. For both kinds of waves, the speed at which the wave travels also depends on the properties of the material through which it is traveling.
Scientists are able to learn about Earth’s internal structure by measuring the arrival of seismic waves at stations around the world. For example, we know that Earth’s outer core is liquid because s-waves are not able to pass through it; when an earthquake occurs there is a “shadow zone” on the opposite side of the earth where no s-waves arrive. Similarly, we know that the earth has a solid inner core because some p-waves are reflected off the boundary between the inner core and the outer core. By measuring the time it takes for seismic waves to travel along many different paths through the earth, we can figure out the velocity structure of the earth. Abrupt changes in velocity with depth correspond to boundaries between different layers of the Earth composed of different materials.
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it captures the sun's energy
Under the leadership of Mikhail Gorbachev, the doctrine of perestroika called for "<span>A. Openness in communication", since the "closed off" Soviet Tactics of the past were clearly not working by the 1980s.</span>
It is called coevolution, when two species influence each other's speciation.
