AMC 10B 2015 Problem 7

Consider the operation minus the reciprocal of, defined by a \diamond b=a-\dfrac{1}{b}. What is ((1 \diamond 2) \diamond 3)-(1 \diamond(2 \diamond 3)) ?

Answer Choices
A. -\dfrac{7}{30}
B. -\dfrac{1}{6}
C. 0
D. \dfrac{1}{6}
E. \dfrac{7}{30}