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Algebra Level 4

What are the roots of the equation \[x^4-(a-b+c+d)x^3+(cd-bc-bd+ac+ad-ab)x^2 \\ -(-bcd+acd-abc-abd)x-abcd=0?\]

\[-a, -b, c, d\] \[-a, b, -c, -d\] \[c,d\] \[b,c\] \[a,d\] \[a, b\] \[a, -b, c, d\] \[a, b, c, d \]