Statements: All poets are readers. Some readers are teachers. Which conclusion necessarily follows?

A little clarity goes a long way.

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  A (Some poets are teachers.):

  The readers who are teachers need not be poets; that overlap is not guaranteed.
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  B (All teachers are poets.):

  The statements give no basis for putting every teacher within the set of poets.
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  C (No poets are teachers.):

  Poets and teachers may overlap; the statements do not rule it out.
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  D (Some teachers are readers.):

  “Some readers are teachers” identifies at least one member of both sets, so some teachers are readers.