Q: In this task, you're given a question, along with three passages, 1, 2, and 3. Your job is to determine which passage can be used to answer the question by searching for further information using terms from the passage. Indicate your choice as 1, 2, or 3.
Question: How many days did the conference in July 1945 last? Passage 1:Silvanus was born in Gaul, the son of Bonitus, a Laetic Frankish general who had supported Constantine I in the civil war against Licinius. Like so many other Franks of his times, and like his father before him, he was a loyal and thoroughly romanized "barbarian" in the military service of the Empire. By AD 351, he held the rank of tribune and was one of the senior officers who defected to Emperor Constantius II at the Battle of Mursa Major, after initially supporting the usurper Magnentius. An able soldier, Silvanus was eventually promoted to the rank of Magister militum per Gallias, a crucial post, then in AD 352-353, Constantius personally entrusted him with the difficult task of driving the Alamanni tribesmen raiding and looting in Gaul back beyond the Rhine, and restoring the fast eroding Roman authority in the province. This Silvanus fulfilled partly by bribing the Alamanni chieftains with the taxes he had collected, partly by defeating the Alamanni in battle and partly by suppressing the local bagaudae insurrections flaring up again in central and northern Gaul.
 Passage 2:Like the star Epsilon Draconis in the constellation of Draco, Beta Cephei is visible primarily in the northern hemisphere, given its extreme northern declination of 70 degrees and 34 minutes. It is nevertheless visible to most observers throughout the world reaching as far south as cities like Harare in Zimbabwe, Santa Cruz de la Sierra in Bolivia or other settlements north ± 19° South latitude. It is circumpolar throughout all of Europe, northern Asia, and North American cities as far south as Guadalajara in west central Mexico. All other locations around the globe having a latitude greater than ± 20° North will notice that the star is always visible in the night sky. Because Beta Cephei is a faint third magnitude star, it may be difficult to identify in most light polluted cities, though in rural locations the star should be easily observable.
 Passage 3:At the Potsdam Conference in July 1945, the Combined Chiefs of Staff decided that Indochina south of latitude 16° north was to be included in the Southeast Asia Command under British Admiral Mountbatten. Japanese forces located south of that line surrendered to him and those to the north surrendered to Generalissimo Chiang Kai-shek. In September 1945, Chinese forces entered Tonkin, and a small British task force landed at Saigon. The Chinese accepted the Vietnamese government under Hồ Chí Minh, then in power in Hanoi. The British refused to do likewise in Saigon, and deferred to the French there from the outset, against the ostensible support of the Việt Minh authorities by American OSS representatives. On V-J Day, September 2, Hồ Chí Minh had proclaimed in Hanoi the establishment of the Democratic Republic of Vietnam (DRV). The DRV ruled as the only civil government in all of Vietnam for a period of about 20 days, after the abdication of Emperor Bảo Đại, who had governed under Japanese rule. On 23 September 1945, with the knowledge of the British commander in Saigon, French forces overthrew the local DRV government, and declared French authority restored in Cochinchina. Guerrilla warfare began around Saigon immediately, but the French gradually retook control of the South and North of Indochina. Hồ Chí Minh agreed to negotiate the future status of Vietnam, but the talks, held in France, failed to produce a solution. After over one year of latent conflict, all-out war broke out in December 1946 between French and Việt Minh forces as Hồ Chí Minh and his government went underground. The French tried to stabilize Indochina by reorganizing it as a Federation of Associated States. In 1949, they put former Emperor Bảo Đại back in power, as the ruler of a newly established State of Vietnam.

A:
3