If a, b, c and d are positive integers and a/b < c/d, which

If a, b, c and d are positive integers and a/b < c/d, which of the following must be true?

I. (a+c)/(b+d) < c/d
II. (a+c)/(b+d) < a/b
III. (a+c)/(b+d) = a/b + c/d

A. None
B. I only
C. II only
D. I and II
E. I and III

Doh! I've seen my mistake now...