Which of the following regions did Alexander von Humboldt not study in his expeditions?

Alexander von Humboldt was a German naturalist and explorer who was a major figure in the classical period of physical geography and biogeography.

In the summer of 1799 he set sail from Marseille accompanied by the French botanist Aimé Bonpland. They spent five years, from 1799 to 1804, in Central and South America, covering more than 6,000 miles (9,650 km) on foot, on horseback, and in canoes.

Starting from Caracas, they traveled south through grasslands and scrublands until they reached the banks of the Apure, a tributary of the Orinoco River. For three months Humboldt and Bonpland moved through dense tropical forests. After a short stay in Cuba, they returned to South America for an extensive exploration of the Andes. From Bogotá to Trujillo, Peru, they wandered over the Andean Highlands

In the spring of 1803, the two travelers sailed from Guayaquil to Acapulco, Mexico, where they spent the last year of their expedition in a close study of this most developed and highly civilized part of the Spanish colonies.

In 1829 Humboldt was given the opportunity to visit Russia and Siberia. The resulting geographical, geological, and meteorological observations, especially those regarding the Central Asian regions, were of great importance to the Western world, for Central Asia was then to a large degree unknown territory.