**Answer**: (B) 2 : 1

**Explanation**:

(a – b)/1 = (b – c)/2 = (c – d)/3 = k (suppose)

hence, (c -d) = 3k or c = d + 3k

also, (b – c) = 2k or b = c + 2k or b = d + 3k + 2k or b = d + 5k

and, (a – b) = k or a = b + k or a = d + 6k

Now, (a + d)/c = (d + 6k + d)/(d + 3k) = 2/1 = 2 : 1