Question

Let I=
integration sign with limit 1 to 2 integration sign with limit 1 to 2 integration sign with limit 1 to 2 integration sign with limit 1 to 2 {(x1 + x2 + x3 - x4)/x1 + x2 + x3 + x4}dx1dx2dx3dx4:
Then I equals
(A) 1/2 (B) 1/3 (C) 1/4 (D) 1