Which expression is equivalent to (x – 1)7? a) x7 – 7x6 – 21x5 – 35x4 – 35x3 – 21x2 – 7x – 1 b) x7 – 7x6 + 21x5 – 35x4 + 35x3 – 21x2 + 7x – 1 c) x7 – 8x6 – 28x5 – 56x4 – 56x3 – 28x2 – 8x – 1 d) x7 – 8x6 + 28x5 – 56x4 + 56x3 – 28x2 + 8x – 1