If \(\dfrac{a}{b}<\dfrac{c}{d}\) and \(bd < 0,\) which of the following inequalities must be true?

I. \(ad -bc < 0\)
II. \(bc -ad > 0\)
III. \(ad -bc > 0\)

A. I only
B. II only
C. III only
D. I and II
E. II and III

Answer: C

Source: e-GMAT