Question: What is the highest elevation in the region that was the Tangs biggest rival?

full_context: Document 1: Sino-Tibetan relations during the Ming dynasty: Discussions of strategy in the mid Ming dynasty focused primarily on recovery of the Ordos region, which the Mongols used as a rallying base to stage raids into Ming China. Norbu states that the Ming dynasty, preoccupied with the Mongol threat to the north, could not spare additional armed forces to enforce or back up their claim of sovereignty over Tibet; instead, they relied on "Confucian instruments of tribute relations" of heaping unlimited number of titles and gifts on Tibetan lamas through acts of diplomacy. Sperling states that the delicate relationship between the Ming and Tibet was "the last time a united China had to deal with an independent Tibet," that there was a potential for armed conflict at their borders, and that the ultimate goal of Ming foreign policy with Tibet was not subjugation but "avoidance of any kind of Tibetan threat." P. Christiaan Klieger argues that the Ming court's patronage of high Tibetan lamas "was designed to help stabilize border regions and protect trade routes."
Document 2: Tibet: Historically, the population of Tibet consisted of primarily ethnic Tibetans and some other ethnic groups. According to tradition the original ancestors of the Tibetan people, as represented by the six red bands in the Tibetan flag, are: the Se, Mu, Dong, Tong, Dru and Ra. Other traditional ethnic groups with significant population or with the majority of the ethnic group residing in Tibet (excluding a disputed area with India) include Bai people, Blang, Bonan, Dongxiang, Han, Hui people, Lhoba, Lisu people, Miao, Mongols, Monguor (Tu people), Menba (Monpa), Mosuo, Nakhi, Qiang, Nu people, Pumi, Salar, and Yi people.
Document 3: Sino-Tibetan relations during the Ming dynasty: Laird writes that the Ming appointed titles to eastern Tibetan princes, and that "these alliances with eastern Tibetan principalities are the evidence China now produces for its assertion that the Ming ruled Tibet," despite the fact that the Ming did not send an army to replace the Mongols after they left Tibet. Yiu Yung-chin states that the furthest western extent of the Ming dynasty's territory was Gansu, Sichuan, and Yunnan while "the Ming did not possess Tibet."
Document 4: Tibet: The Tibetan name for their land, Bod བོད་, means "Tibet" or "Tibetan Plateau", although it originally meant the central region around Lhasa, now known in Tibetan as Ü. The Standard Tibetan pronunciation of Bod, [pʰøʔ˨˧˨], is transcribed Bhö in Tournadre Phonetic Transcription, Bö in the THL Simplified Phonetic Transcription and Poi in Tibetan pinyin. Some scholars believe the first written reference to Bod "Tibet" was the ancient Bautai people recorded in the Egyptian Greek works Periplus of the Erythraean Sea (1st century CE) and Geographia (Ptolemy, 2nd century CE), itself from the Sanskrit form Bhauṭṭa of the Indian geographical tradition.
Document 5: Tibet: The Indus and Brahmaputra rivers originate from a lake (Tib: Tso Mapham) in Western Tibet, near Mount Kailash. The mountain is a holy pilgrimage site for both Hindus and Tibetans. The Hindus consider the mountain to be the abode of Lord Shiva. The Tibetan name for Mt. Kailash is Khang Rinpoche. Tibet has numerous high-altitude lakes referred to in Tibetan as tso or co. These include Qinghai Lake, Lake Manasarovar, Namtso, Pangong Tso, Yamdrok Lake, Siling Co, Lhamo La-tso, Lumajangdong Co, Lake Puma Yumco, Lake Paiku, Lake Rakshastal, Dagze Co and Dong Co. The Qinghai Lake (Koko Nor) is the largest lake in the People's Republic of China.
Document 6: Tibet: The language has numerous regional dialects which are generally not mutually intelligible. It is employed throughout the Tibetan plateau and Bhutan and is also spoken in parts of Nepal and northern India, such as Sikkim. In general, the dialects of central Tibet (including Lhasa), Kham, Amdo and some smaller nearby areas are considered Tibetan dialects. Other forms, particularly Dzongkha, Sikkimese, Sherpa, and Ladakhi, are considered by their speakers, largely for political reasons, to be separate languages. However, if the latter group of Tibetan-type languages are included in the calculation, then 'greater Tibetan' is spoken by approximately 6 million people across the Tibetan Plateau. Tibetan is also spoken by approximately 150,000 exile speakers who have fled from modern-day Tibet to India and other countries.
Document 7: Tibet: The Tibetan Empire emerged in the 7th century, but with the fall of the empire the region soon divided into a variety of territories. The bulk of western and central Tibet (Ü-Tsang) was often at least nominally unified under a series of Tibetan governments in Lhasa, Shigatse, or nearby locations; these governments were at various times under Mongol and Chinese overlordship. The eastern regions of Kham and Amdo often maintained a more decentralized indigenous political structure, being divided among a number of small principalities and tribal groups, while also often falling more directly under Chinese rule after the Battle of Chamdo; most of this area was eventually incorporated into the Chinese provinces of Sichuan and Qinghai. The current borders of Tibet were generally established in the 18th century.
Document 8: Tibet: Tibet has some of the world's tallest mountains, with several of them making the top ten list. Mount Everest, located on the border with Nepal, is, at 8,848 metres (29,029 ft), the highest mountain on earth. Several major rivers have their source in the Tibetan Plateau (mostly in present-day Qinghai Province). These include the Yangtze, Yellow River, Indus River, Mekong, Ganges, Salween and the Yarlung Tsangpo River (Brahmaputra River). The Yarlung Tsangpo Grand Canyon, along the Yarlung Tsangpo River, is among the deepest and longest canyons in the world.
Document 9: Tibet: Tibet (i/tᵻˈbɛt/; Wylie: Bod, pronounced [pʰø̀ʔ]; Chinese: 西藏; pinyin: Xīzàng) is a region on the Tibetan Plateau in Asia. It is the traditional homeland of the Tibetan people as well as some other ethnic groups such as Monpa, Qiang and Lhoba peoples and is now also inhabited by considerable numbers of Han Chinese and Hui people. Tibet is the highest region on Earth, with an average elevation of 4,900 metres (16,000 ft). The highest elevation in Tibet is Mount Everest, earth's highest mountain rising 8,848 m (29,029 ft) above sea level.
Document 10: Sino-Tibetan relations during the Ming dynasty: Patricia Ebrey writes that Tibet, like Joseon Korea and other neighboring states to the Ming, settled for its tributary status while there were no troops or governors of Ming China stationed in its territory. Laird writes that "after the Mongol troops left Tibet, no Ming troops replaced them." Wang and Nyima state that, despite the fact that the Ming refrained from sending troops to subdue Tibet and refrained from garrisoning Ming troops there, these measures were unnecessary so long as the Ming court upheld close ties with Tibetan vassals and their forces. However, there were instances in the 14th century when the Hongwu Emperor did use military force to quell unrest in Tibet. John D. Langlois writes that there was unrest in Tibet and western Sichuan, which the Marquis Mu Ying (沐英) was commissioned to quell in November 1378 after he established a Taozhou garrison in Gansu. Langlois notes that by October 1379, Mu Ying had allegedly captured 30,000 Tibetan prisoners and 200,000 domesticated animals. Yet invasion went both ways; the Ming general Qu Neng, under the command of Lan Yu, was ordered to repel a Tibetan assault into Sichuan in 1390.
Document 11: Tibet: The modern Standard Chinese exonym for the ethnic Tibetan region is Zangqu (Chinese: 藏区; pinyin: Zàngqū), which derives by metonymy from the Tsang region around Shigatse plus the addition of a Chinese suffix, 区 qū, which means "area, district, region, ward". Tibetan people, language, and culture, regardless of where they are from, are referred to as Zang (Chinese: 藏; pinyin: Zàng) although the geographical term Xīzàng is often limited to the Tibet Autonomous Region. The term Xīzàng was coined during the Qing dynasty in the reign of the Jiaqing Emperor (1796–1820) through the addition of a prefix meaning "west" (西 xī) to Zang.
Document 12: Mount Everest: Mount Everest, known in Nepali as Sagarmatha (सगरमाथा) and in Tibetan as Chomolungma (ཇོ ་ མོ ་ གླང ་ མ), is Earth's highest mountain above sea level, located in the Mahalangur Himal sub-range of the Himalayas. The international border between Nepal (Province No. 1) and China (Tibet Autonomous Region) runs across its summit point.
Document 13: Sino-Tibetan relations during the Ming dynasty: During the Five Dynasties and Ten Kingdoms period of China (907–960), while the fractured political realm of China saw no threat in a Tibet which was in just as much political disarray, there was little in the way of Sino-Tibetan relations. Few documents involving Sino-Tibetan contacts survive from the Song dynasty (960–1279). The Song were far more concerned with countering northern enemy states of the Khitan-ruled Liao dynasty (907–1125) and Jurchen-ruled Jin dynasty (1115–1234).
Document 14: Tibet: In 821/822 CE Tibet and China signed a peace treaty. A bilingual account of this treaty, including details of the borders between the two countries, is inscribed on a stone pillar which stands outside the Jokhang temple in Lhasa. Tibet continued as a Central Asian empire until the mid-9th century, when a civil war over succession led to the collapse of imperial Tibet. The period that followed is known traditionally as the Era of Fragmentation, when political control over Tibet became divided between regional warlords and tribes with no dominant centralized authority.
Document 15: Sino-Tibetan relations during the Ming dynasty: Tibet was once a strong power contemporaneous with Tang China (618–907). Until the Tibetan Empire's collapse in the 9th century, it was the Tang's major rival in dominating Inner Asia. The Yarlung rulers of Tibet also signed various peace treaties with the Tang, culminating in a treaty in 821 that fixed the borders between Tibet and China.
ground_truth: Mount Everest
sub_queries: Who was the Tangs biggest rival? Answer: Tibet
What is the highest elevation in Tibet ? Answer: Mount Everest