The oxides of nitrogen, nitric oxide, NO, and nitrogen dioxide, NO2, are both collectively known as NOx, and are familiar as one of the several components of automobile exhaust that create smog. In the hot combustion chambers of a car's engine, N2 and O2 react together to form NO.
The three pyramids of Giza are the most famous. They were built in the 26th century B.C. The largest pyramid of Giza is called the Great Pyramid of Khufu. It is also the largest and grandest pyramid ever built. It is 479 feet tall (146 meters). The pharaoh Sneferu built this pyramid for his son, Khufu, in 2540 B.C. It was built from millions of blocks of limestone and granite.
Egypt's Great Pyramids at Giza are one of the world's most amazing achievements. Built during the reign of Cheops, around 2530 B.C., the largest pyramid towers nearly 500 feet (150 meters) high and covers 13 acres (5.2 hectares).