let A= a+b-2c , -B= 2a-b-c , C= a-2b+c

we have A+B +C= = 0

So -B = A +C

so discriminant = (A+C)^2-4AC =(A-C)^2 = (3(b-c))^2

so roots are x= (2a-b-c)+-(3(b-c))/(2(a+b-2c))

on calculation it becomes 1 and (a-2b+c)/(a+b-2c)

so I think it is (d)

But plz check the calculation the trick remaining the same .