Given the task definition and input, reply with output. In this task, you're given a question, along with a context passage. The passage will not have a direct answer to the question, but can include some information and a clue for the answer. Assuming you can only obtain information about one entity in the passage, your job is to determine whether information from the passage can be used to answer the question. Indicate your choice as 'a' for Yes or 'b' for No.

Question: What was the combined population of Bessarabia and Wallachian Plain during the formation of Bulgaria? 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.
a