An aqueous buffer is prepared by adding 100 ml of 0.1 mol l-1 acetic acid to 50 ml of 0.2 mol l-1 of sodium acetate. If pKa of acetic acid is 4.76, the pH of the buffer is
option
(A) 4.26
(B) 5.76
(C) 3.76
(D) 4.76