Which polynomial is prime?

A polynomial is prime here if it cannot be factored into polynomials with integer coefficients. Choice B, x² + 6, has no integer factors: there are no integers whose product is 6 and whose sum is 0. The other choices factor: x² − x − 20 = (x − 5)(x + 4), x² − 36 = (x − 6)(x + 6), and x² − 7x + 12 = (x − 3)(x − 4).

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