Which expression is prime?a.x2 + 3x + 2b.x2 + 8x + 7c.x2 + 8x - 22d.x2 + 12x + 27?

Prime means it cannot be factored any more. 
the answer is C
A=(x+1)(x+2)
B=(x+1)(x+7)
D=(x+3)(x+9)
But C cannot be factored. If it were x²+9x-22, it would be (x+11)(x-2). but with 8x, it doesn't work.