A word-and-number arrangement machine, when given an input line of words and numbers, rearranges it in steps. In each step the machine takes the smallest of the numbers that are divisible by 3 and have not already been shifted, and places it at the extreme left end of the line. Numbers not divisible by 3, and all the words, are never shifted; every other element keeps its relative position, and the machine stops once every number divisible by 3 has been shifted. Input: beans 72 rice 45 noodles 58 pudding 21. Which of the following is the last step of the above arrangement?

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72 45 21 beans rice noodles 58 pudding. The multiples of 3 are 21, 45 and 72; 58 is not one. Step 1: 21 beans 72 rice 45 noodles 58 pudding. Step 2: 45 21 beans 72 rice noodles 58 pudding. Step 3 (last): 72 45 21 beans rice noodles 58 pudding. "21 45 72 beans rice noodles 58 pudding" reads the left block in ascending order, which would need the numbers to be added from the right of the block rather than in front of it. "45 21 beans 72 rice noodles 58 pudding" stops one step early, at Step 2. "72 58 45 21 beans rice noodles pudding" shifts 58 as well, although 58 is not divisible by 3.

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