Of the N students in a certain class, X took a course in biology and Y took a course in history, and Z took neither of the courses. If there were students who took both two courses, in terms of N, X, Y and Z, what fraction of the students took both two courses?
(A) 1 - (X+Y+Z) / N
(B) (X+Y+Z) / N - 1
(C) (X+Y-Z-N) / N
(D) (N+X+Y-Z) / N
(E) (N-X-Y+Z) / N
(A) 1 - (X+Y+Z) / N
(B) (X+Y+Z) / N - 1
(C) (X+Y-Z-N) / N
(D) (N+X+Y-Z) / N
(E) (N-X-Y+Z) / N