Question: Which landlocked country in South Asia and one of the region's least populous nations has only four airports?

Context paragraphs:
Landlocked developing countries: Landlocked developing countries (LLDC) are developing countries that are landlocked.  The economic and other disadvantages experienced by such countries makes the majority of landlocked countries least developed countries (LDC), with inhabitants of these countries occupying the bottom billion tier of the world's population in terms of poverty.  Apart from Europe, there is not a single successful highly developed landlocked country as measured by the Human Development Index (HDI), and nine of the twelve countries with the lowest HDI scores are landlocked.  Landlocked European countries are exceptions in terms of development outcomes due to their close integration with the regional European market.  Landlocked countries that rely on transoceanic trade usually suffer a cost of trade that is double that of their maritime neighbours.  Landlocked countries experience economic growth 6% less than their non-landlocked countries, holding other variables constant.

Eastern South Asia: Eastern South Asia is a subregion of South Asia.  It includes the countries of Bangladesh, Bhutan, India (specifically east India and northeast India), and Nepal.  Geographically, it lies between the Eastern Himalayas and the Bay of Bengal.  Two of the world's largest rivers, the Ganges and the Brahmaputra, flow into the sea through Eastern South Asia.  The region includes the world's highest mountainous terrain and the world's largest delta, and has a climate ranging from alpine and subalpine to subtropical and tropical.  Since Nepal, Bhutan, and northeast India are landlocked, the coastlines of Bangladesh and East India serve as the principal gateways to the region.

Transport in Bhutan: Transport in Bhutan comprises approximately 8000 km of roads and four airports, out of which 3 are operational and interconnected.  Paro Airport is the only airport that serves international flights.  As part of Bhutan's infrastructure and modernization programs, its road system has been under development since the 1960s.  There are no railways, although one is planned, and as Bhutan is a landlocked country without major waterways, there are no ports.

Bhutan: Bhutan ( ; འབྲུག་ཡུལ་ "druk yul "), officially the Kingdom of Bhutan (འབྲུག་རྒྱལ་ཁབ་ "druk gyal khap "), is a landlocked country in South Asia.  Located in the Eastern Himalayas, it is bordered by Tibet Autonomous Region in the north, India in the south, the Sikkim state of India and the Chumbi Valley of Tibet in the west, and Arunachal Pradesh state of India in the east.  Bhutan is geopolitically in South Asia and is the region's second least populous nation after the Maldives.  Thimphu is its capital and largest city, while Phuntsholing is its financial center.

Paraguay: Paraguay ( ; ] ; Guarani: "Paraguái" , ] ), officially the Republic of Paraguay (Spanish: "República del Paraguay" ; Guarani: "Tetã Paraguái" ), is a landlocked country in central South America, bordered by Argentina to the south and southwest, Brazil to the east and northeast, and Bolivia to the northwest.  Paraguay lies on both banks of the Paraguay River, which runs through the center of the country from north to south.  Due to its central location in South America, it is sometimes referred to as "Corazón de Sudamérica" ("Heart of South America").  Paraguay is one of the two landlocked countries (the other is Bolivia) outside Afro-Eurasia, and is the smallest landlocked country in the Americas.

Invasions of Afghanistan: Afghanistan is a mountainous landlocked country in Central Asia and South Asia.  The Afghanistan area has been invaded many times in recorded history, but no invader has been able to control all of its regions at the same time, and at some point faced rebellion.  Some of the invaders in the history of Afghanistan include the Maurya Empire of ancient India, Alexander the Great of Macedon, Umar, an Arab Caliphate, Genghis Khan of Mongolia, Timur of Persia and Central Asia, the Mughal Empire of India, various Persian Empires, the British Empire, the Sikh Empire, the Soviet Union, and most recently a coalition force of NATO troops, the majority from the United States, which entered the country in the first-ever invocation of NATO's Article 5 "an attack on one is an attack on all" following the September 11 attacks in the United States.  The country is now entitled the Islamic Republic of Afghanistan and has a democratically elected government.  A reduced number of NATO troops remain in the country in support of the government under the U.S.–Afghanistan Strategic Partnership Agreement.

Mugu District: Mugu District (Nepali:    , a part of Province No. 6, is one of the seventy-five districts of Nepal, a landlocked country of South Asia.  The district, with Gamgadhi as its district headquarters, covers an area of 3,535 km² and had a population (2011) of 55,286.  Mugu is known for being both the most remote district in Nepal, as well as the least developed.

Yongphulla Airport: Yongphulla Airport (IATA: YON, ICAO: VQTY) (also known as Yonphula Airport) is a domestic airport in Bhutan, one of only four airports in the country.  It is located near the town of Trashigang in Trashigang District.  As of January 2015, the airport remains closed due to ongoing runway repair.

Afghanistan: Afghanistan ( ; Pashto/Dari: , Pashto: "Afġānistān" ] , Dari: "Afġānestān" ] ), officially the Islamic Republic of Afghanistan, is a landlocked country located within South Asia and Central Asia.  The country has a population of /1e6 round 0 million, making it the 42nd most populous country in the world.  Afghanistan is bordered by Pakistan in the south and east; Iran in the west; Turkmenistan, Uzbekistan, and Tajikistan in the north; and China in the far northeast.  Its territory covers 652,000 km2 , making it the 41st largest country in the world.

List of companies of Afghanistan: Afghanistan is a landlocked country located within South Asia and Central Asia.  It has a population of approximately 32 million, making it the 42nd most populous country in the world.  It is bordered by Pakistan in the south and east; Iran in the west; Turkmenistan, Uzbekistan, and Tajikistan in the north; and China in the far northeast.  Its territory covers 652,000 km2 , making it the 41st largest country in the world.

Supporting paragraphs: Yongphulla Airport Bhutan
Answer: Bhutan