Which river crosses the Equator twice in its course?

The correct answer is B, the Nile. At a little over 6,600 kilometres it is the river that standard references and examination papers treat as the longest, flowing north through Sudan and Egypt into the Mediterranean Sea from two branches, the White Nile of the Lake Victoria region and the Blue Nile of Lake Tana in Ethiopia. Option A, the Amazon, is second in length but first in volume and in basin area, and the distinction between longest and largest is exactly what the question is testing. Option C, the Yangtze, is the longest river of Asia and the third longest in the world, and the Three Gorges Dam stands on it. Option D, the Mississippi, with the Missouri forms the longest system of North America and drains into the Gulf of Mexico, but it is well short of the Nile. Read the question with care, because a paper asking for the largest river expects the Amazon instead.

The correct answer is B, Khartoum, the capital of Sudan, where the two great branches of the Nile join and flow on as a single river towards Egypt. The White Nile comes from the Lake Victoria region of East Africa and carries a steady flow; the Blue Nile rises at Lake Tana in the Ethiopian highlands and brings the summer flood and most of the silt. Option A, Cairo, lies far downstream in Egypt, close to where the Nile opens into its delta. Option C, Addis Ababa, is the capital of Ethiopia and stands on no part of the Nile channel, although the Blue Nile rises in that country. Option D, Aswan, is the Egyptian town known for the Aswan High Dam and Lake Nasser behind it, again downstream of the confluence. The pairing to carry into the hall is Lake Tana with the Blue Nile and Khartoum with the confluence.

The correct answer is C, the Andes. The range runs about 7,000 kilometres down the western edge of South America through Venezuela, Colombia, Ecuador, Peru, Bolivia, Chile and Argentina, and it carries Aconcagua, the highest peak outside Asia. Option A, the Himalaya, is the highest range in the world and holds Mount Everest, but it is far shorter, stretching roughly 2,400 kilometres from the Indus to the Brahmaputra. Option B, the Rockies, runs from Canada to the south-western United States and is also shorter than the Andes. Option D, the Great Dividing Range, follows the eastern side of Australia and holds Mount Kosciuszko, the highest point of the Australian mainland. Note the word continental in the question: if ranges on the sea floor are allowed, the mid-oceanic ridge is many times longer than the Andes and becomes the right answer.

The correct answer is C, Argentina. Aconcagua stands in the Andes in the Mendoza region of western Argentina, close to the Chilean border, and at about 6,961 metres it is the highest summit of both the Americas and of the southern hemisphere, and so the highest anywhere outside Asia. Option A, Chile, holds the long western slope of the Andes and many high volcanoes such as Ojos del Salado, which is the highest volcano on earth, but Aconcagua itself lies on the Argentine side of the frontier. Option B, Peru, has the Cordillera Blanca with Huascaran, high but lower than Aconcagua. Option D, Bolivia, holds the Altiplano and peaks such as Nevado Sajama, again lower. Keep the set of continental high points together: Everest for Asia, Aconcagua for South America, Denali for North America, Kilimanjaro for Africa, Elbrus for Europe and Vinson Massif for Antarctica.

The correct answer is B, the Sahara, which stretches across North Africa through about eleven countries from the Atlantic coast to the Red Sea and is the largest hot desert on earth. Option A, the Gobi, lying in Mongolia and northern China, is the largest desert of Asia but a cold desert, with freezing winters, so it fails the word hot in the question. Option C, the Kalahari, in Botswana, Namibia and South Africa, is hot but much smaller than the Sahara and is in large part a sandy savanna that supports grass and thorn. Option D, the Great Victoria Desert, is the largest desert of Australia and again far smaller. Remember that if the question drops the word hot and asks only for the largest desert, the answer becomes the Antarctic Desert, because geographers define a desert by low precipitation and not by temperature.