Correct: A. China

The Yarlung Tsangpo Grand Canyon is the deepest canyon in the world and is located in the Tibet Autonomous Region of China. It is carved by the Yarlung Tsangpo River as it flows around the high peaks of the Himalayas, reaching a maximum depth of over 6,000 meters (19,000 feet)-making it significan'tly deeper than the Grand Canyon in the United States.

Correct: D. Ireland

The Giant's Causeway is a famous natural formation of about 40,000 interlocking basalt columns located on the north coast of Northern Ireland. It was created roughly 50 to 60 million years ago by ancient volcanic activity, which caused molten lava to cool and crack into perfect hexagonal shapes. According to local legend, the causeway was built by the Irish giant Finn MacCool so he could walk across the sea to fight a Scottish rival.

Correct: B. Arabian

The Arabian Peninsula is the largest peninsula in the world, covering an area of approximately 1.25 million square miles 3.2 million km. It is located in the Middle East and is surrounded by the Red Sea to the west, the Persian Gulf to the east, and the Arabian Sea to the south. The region is of immense global importance due to its vast oil and gas reserves and its central role in the history of Islam.

Correct: B. Central Asia

The Tian Shan mountains, which means "Celestial Mountains" in Chinese, are a large system of mountain ranges located primarily in the border region of China, Kazakhstan, Kyrgyzstan, and Uzbekistan. They form part of the great Himalayan mountain belt and contain some of the highest peaks in the world outside of the Himalayas and Karakoram. The range is a UNESCO World Heritage site and has historically been a major corridor for the Silk Road.

Correct: B. Scoresby Sund

Scoresby Sund in Greenland is the world's longest and largest fjord system - extending approximately 350 km inland from the coast. Sognefjord in Norway at 204 km is the world's longest fjord in Norway and Europe.

Correct: B. Arica

Arica in northern Chile is considered the world's driest inhabited city - it receives an average of approximately 0.8 mm of rain per year and has recorded no rainfall for years at a time. It lies in the Atacama Desert near the Peruvian border.

Correct: C. Yosemite

Yosemite National Park in California typically ranks among the most visited US national parks along with the Great Smoky Mountains. The Great Smoky Mountains (Tennessee/North Carolina) actually typically receives the most visitors - approximately 12-13 million annually.

Correct: A. Sarawak Chamber

The Sarawak Chamber in Gunung Mulu National Park, Borneo, Malaysia, is the world's largest cave chamber by floor area - approximately 600 metres long, 415 metres wide, and at least 80 metres high (approximately 600 million cubic metres volume).

Correct: D. Majuli

Majuli in the Brahmaputra River in Assam, India, is the world's largest river island - covering approximately 880-1,250 square kilometres (its area has been shrinking due to erosion). It became India's first island district in 2016.

Correct: D. Kiritimati

Kiritimati (Christmas Island) in Kiribati is the world's largest atoll by land area - covering approximately 321 square kilometres, comprising approximately 70% of the land area of Kiribati.

Correct: D. Cerro Llullaillaco

Cerro Llullaillaco on the Chile-Argentina border is the world's highest active volcano at 6,739 metres - it last erupted in 1877. Near its summit archaeologists discovered three Inca children sacrificed approximately 500 years ago - the best-preserved human mummies ever found, preserved by the extreme cold and altitude.

Correct: A. Sistema Ox Bel Ha

Sistema Ox Bel Ha in Mexico's Yucatan Peninsula is one of the world's longest cave systems - primarily a submerged underwater (anchialine) cave system with approximately 270+ km of surveyed passages accessible by cave divers. Lechuguilla Cave in New Mexico is among the longest non-submerged caves.

Correct: C. Great Basin

The Great Basin in the western United States is the largest endorheic (internally draining) basin in North America - covering approximately 492,000 square kilometres across Nevada, Utah, California, Idaho, and Oregon. Rivers drain inward rather than to the sea.

Correct: C. Cape Fold Belt

The Cape Fold Belt in South Africa is one of Earth's oldest mountain systems - formed approximately 250-330 million years ago and containing one of the world's most biodiverse plant communities. The Cape Floristic Region has approximately 9,000 plant species - 70% found nowhere else.

Correct: B. An Nafud

The An Nafud desert in Saudi Arabia and the Rub' al Khali (Empty Quarter) are large sand seas - the Rub' al Khali at approximately 650,000 km is the world's largest continuous sand desert. However specific erg (sand sea) rankings vary by definition.

Correct: B. Toba

Lake Toba in Sumatra, Indonesia, occupies the world's largest volcanic caldera formed by a supervolcanic eruption approximately 74,000 years ago - the largest volcanic eruption in the past 2 million years. The caldera measures approximately 100 - 30 km.

Correct: D. Odahraun

The Odahraun (Evil Deeds Lava) is Iceland's largest lava field - covering approximately 3,400 square kilometres in the central highland interior. Iceland contains some of the world's most extensive lava fields as a result of its volcanic activity.

Correct: B. Frying Pan Lake

The Frying Pan Lake (Waimangu Cauldron) in Rotorua is the world's largest hot spring - covering approximately 38,000 square metres and maintained at approximately 55C. The Waimangu Volcanic Valley where it sits was created by the 1886 eruption of Mount Tarawera.

Correct: B. Valdivian Temperate Rainforest

The Valdivian Temperate Rainforest in southern Chile and a small area of Argentina is the world's largest temperate rainforest in the Southern Hemisphere - covering approximately 248,100 square kilometres. It is characterised by ancient alerce trees (some over 4,000 years old).