Let the sum of binomial coefficients in the expansion of (a-b) n be 256, then the term with the smallest coefficient in the binomial expansion is () A. Item 5 B. items 4 and 5 C. items 5 and 6 D. items 4 and 6

Let the sum of binomial coefficients in the expansion of (a-b) n be 256, then the term with the smallest coefficient in the binomial expansion is () A. Item 5 B. items 4 and 5 C. items 5 and 6 D. items 4 and 6

According to the solution of 2n = 256, the general term of the expansion of n = 8 ∫ (a-b) n = (a-b) 8 ∫ (a-b) 8 is tr + 1 = (- 1) rc8ra8 RBR, where r = 0, 1, 2, 3, 4, 5, 6, 7, 8 ∫ when r = 3, 5, the coefficient is the smallest, that is, the coefficient of the fourth and sixth terms is the smallest