In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

[Q]: Tibet's incursions into Sichuan can be classified as what during the Tang Dynasty?, Context: Sichuan came under the firm control of a Chinese central government during the Sui dynasty, but it was during the subsequent Tang dynasty where Sichuan regained its previous political and cultural prominence for which it was known during the Han. Chengdu became nationally known as a supplier of armies and the home of Du Fu, who is sometimes called China's greatest poet. During the An Lushan Rebellion (755-763), Emperor Xuanzong of Tang fled from Chang'an to Sichuan. The region was torn by constant warfare and economic distress as it was besieged by the Tibetan Empire.
[A]: constant


[Q]: On what planet are the countries that import Guinea-Bissau's exports located?, Context: Guinea-Bissau's GDP per capita is one of the lowest in the world, and its Human Development Index is one of the lowest on earth. More than two-thirds of the population lives below the poverty line. The economy depends mainly on agriculture; fish, cashew nuts and ground nuts are its major exports.
[A]: earth


[Q]: After which event did Ottoman forces capture Calafat?, Context: Following the Ottoman ultimatum in September 1853, forces under the Ottoman general Omar Pasha crossed the Danube at Vidin and captured Calafat in October 1853. Simultaneously, in the east, the Ottomans crossed the Danube at Silistra and attacked the Russians at Oltenița. The resulting Battle of Oltenița was the first engagement following the declaration of war. The Russians counterattacked, but were beaten back. On 31 December 1853, the Ottoman forces at Calafat moved against the Russian force at Chetatea or Cetate, a small village nine miles north of Calafat, and engaged them on 6 January 1854. The battle began when the Russians made a move to recapture Calafat. Most of the heavy fighting, however, took place in and around Chetatea until the Russians were driven out of the village. Despite the setback at Chetatea, on 28 January 1854, Russian forces laid siege to Calafat. The siege would continue until May 1854 when the Russians lifted the siege. The Ottomans would also later beat the Russians in battle at Caracal.:130–43
[A]:
the Ottoman ultimatum in September 1853