Why is a transistor classified as a semiconductor? it behaves like a switch in a circuit. it conducts electricity in a circuit. it has controlled impurities to vary its conductivity. it increases the amplitude of an applied signal.

A transistor is not 'classified' as a semiconductor. A transistor is MADE from semiconductor materials. Those are materials that have controlled amounts of impurities that allow their conductivity to be controlled. This behavior of their constituent materials is what makes transistors work.

the arctic is a region of the planet, north of the arctic circle, and includes the arctic ocean, greenland, baffin island, other smaller northern islands, and the far northern parts of europe, russia (siberia), alaska and canada.