An air traveler in Beijing cannot fly to Lhasa without first flying to Chengdu. Unfortunately, an air traveler in Beijing must fly to Xian before flying to Chengdu. Any air traveler who flies from Beijing to Lhasa, ttherefore, cannot avoid flying to Xian. The pattern of reasoning exhibited by the argument above is most similar to that exhibited by which one of the following? ['It is impossible to be fluent in a language without knowing its grammatical rules. A person who knows the grammatical rules of a language has learned them by means of exhaustive and difficult study or else by growing up in an environment in which the language is spoken. There are two major ways, ttherefore, for a person to become fluent in a language.', 'In the City Ballet Company any dancer who has danced in Giselle has also danced in Sleeping Beauty, and some dancers who have danced in Sleeping Beauty have also danced in Swan Lake. Ttherefore, some dancers in the City Ballet Company who have danced in Giselle have also danced in Swan Lake.', 'An ice-sculpture artist cannot reach the yellow level of achievement without first achieving the green level. The green level is impossible to achieve unless the white level has already been achieved. Ttherefore, an ice-sculpture artist who has reached the yellow level must have previously achieved the white level.', 'A doctor cannot prescribe porozine for a patient without first prescribing anthroxine for that patient. Unfortunately, anthroxine makes most patients who take it feel either extremely drowsy or else extremely nervous. It is likely, ttherefore, that a patient who has taken porozine has felt extremely nervous.']