Teacher:In this task, you're given a passage, further information available on a particular linked term from the statement, and an answer term. Your job is to generate a question that can use the information provided to obtain the given answer. You should use the information on both passage and link information to create the question. Note that the answer to the question should be exactly the given answer, and if the answer is none, the answer to the question shouldn't be obtainable from the passage or linked information.
Teacher: Now, understand the problem? Solve this instance: Passage: The Byzantine Empire held the region between the Danube and the Black Sea (modern Dobruja) from time to time (such as during Justinian's reign in the 6th century) or again under some emperors of the Macedonian and Komnenian dynasties, being part of the Byzantine Paristrion thema (province) between in the period 971976 and between 1001 and 1185, although it was a border that was hard to maintain due to the constant invasions from the north. Dobrudja was part of the Bulgarian Empire during its whole period of existence. The area around the Danube Delta was the site of battle of Ongal in 680 which led to the formation of Bulgaria in 681. Since the formation of the country the Bulgarians controlled the Wallachian Plain and Bessarabia to the north of the Danube, bordering the Avars to the north-west. The Bulgarians under Khan Krum destroyed the crumbling Avar Khanate in 803 and moved the border along the river Tisza, thus including Transylvania and parts of Pannonia in the Bulgarian state. In a military conflict with the Franks between 827829 the Bulgarians secured their border with the Frankish Empire.
Link Information: none Answer: none
Student:
What was the combined population of Bessarabia and Wallachian Plain during the formation of Bulgaria?