A, B and C sit in a row facing north. A sits immediately to the left of B, and B immediately to the left of C. Who sits in the middle?

A little clarity goes a long way.

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  A (A):

  A is the leftmost person in the uniquely determined order A–B–C.
• •
  B (B):

  The clues establish A–B–C from left to right, placing B in the middle.
• •
  C (C):

  C is the rightmost person, not the middle person.
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  D (Cannot be determined):

  The two immediate-left relationships determine all three positions; no additional clue is needed.