In a marketing survey, 60 people were asked to rank three flavors of ice cream, chocolate, vanilla, and strawberry, in order of their preference. All 60 people responded, and no two flavors were ranked equally by any of the people surveyed. If 3/5 of the people ranked vanila last, 1/10 of them ranked vanila before chocolate, and 1/3 of them ranked vanilla before strawberry, how many people ranked vanilla first?
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正确答案: A