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.
Q: Question: How long had Stalin been the leader of the Soviet Union by the year 1937? Passage 1:Inside the SAPD, the first part of 1937 saw an intensification of differences over attitudes to a possible political party of the united left or a Popular front, and more precisely over the party's approach to the Soviet Union. The differences led to Peter Blachstein's exclusion from the SAPD. Others excluded at the same time included his political mentor and Erwin Ackerknecht: the three became the focus of a short-lived political grouping known as "Neuer Weg" ("New Way"). Blachstein was also affected more directly by the intense political tensions radiating out from Moscow, based on Stalin's suspicions - not entirely unfounded - that there might be comrades in the Soviet Union and further west in Europe who favoured an alternative Soviet leader. The POUM, of which Blachstein was a member, backed a broadly Trotskyite vision for a communist future and its members therefore became targets for Soviet agents. In June 1937 Blachstein was arrested in Barcelona by communist secret police and accused of spying for Franco and working for the Gestapo. With approximately 100 other foreign detainees he was taken to a large garage which had been adapted for use as an ad hoc prison. Because of the appalling hygiene he soon fell ill with Tuberculosis, as a result of which he was transferred to a sanatorium controlled by anarchist comrades. Helped by Spanish friends, in January 1938 he succeeded in escaping back to France.
 Passage 2:Thalassocnus were ground sloths that lived from the Late Miocene to the end of the Pliocene—Late Huayquerian to Early Uquian in the SALMA classification—and all five species were discovered in different horizons of the Pisco Formation in Peru. T antiquus was discovered in the Aguada de Lomas Horizon in 7 or 8 million year old strata; T. natans (the type species) from the Montemar Horizon lived around 6 million years ago (mya); T. littoralis from the Sud-Sacaco Horizon lived around 5 mya; T. carolomartini from the Sacaco Horizon lived between 3 and 4 mya; and T. yaucensis from the Yuaca Horizon lived 3 to 1.5 mya. Specimens were also found in the Bahía Inglesa Formation, the Coquimbo Formation, and the Horcón Formation in Chile. At total of three species has been identified with certainty in Chilean formations, T. carolomartini, T. natans, T. Antiquus while the presence of T. yaucensis is judged likely. 
 Passage 3:"The Lazy Song" has received generally mixed reviews from contemporary music critics. Eric Henderson of Slant Magazine noted that in song Mars "paints a portrait of Al Bundy as a young man" and Andy Gill of The Independent classified the song as a "laidback acoustic groove". Tim Sendra of AllMusic said it was one of the tracks from Doo-Wops & Hooligans that captured the laid-back groove. Scott Mervis of the Pittsburgh Post-Gazette described the song as a "Jason Mraz/Sugar Ray-style reggae." Sean Fennessey, a reviewer of The Washington Post, felt the song was written in a "quality that is both endearing and damning". A mixed review came from Digital Spy reviewer Lewis Corner, who commented that the song is a "summery ditty more head-boppable than a Churchill nodding dog, which, given his current state of mind, is probably about all he could muster", giving it three stars out of five. and from Blues & Soul magazine who called it "reggae tinged" and found it to be "somewhat of a filler but for the likes of Peter Andre" is great. Entertainment Weeklys Leah Greenblatt considered that "other modes suit him less well; The Lazy Song is perhaps better left to Jason Mraz". Alexis Petridis of The Guardian, gave the song a negative review, writing that "The Lazy Song" "gets no further than the second verse before Mars – nothing if not keen to keep his fans abreast of his every activity in a world of 360-degree connectivity – announces that he's planning on having a wank". Nick Messitte writing for Forbes criticized the single for copying the "happy-go-lucky meanderings of Jason Mraz's "I'm Yours", but also using the same pattern as Travie McCoy and Mars' "Billionaire" (2011).

A:
1