Define and explain the significance of longitude

Latitude and longitude are imaginary lines that help us label every place on the surface of the earth. The most important line of latitude is the equator, which runs horizontally around the fattest part of the earth. The most important longitude line is the Prime Meridian which runs vertically and goes through Greenwich, England. Another important longitude line is the international date line, which goes vertically through the middle of the ocean opposite the Prime Meridian. Hope It Helps

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The answer is d., a mountain.