Suppose a and b are single-digit positive integers chosen independently and at random. What is the probability that the point (a, b) lies above the parabola y=a x^{2}-b x ?
Answer Choices
A. \dfrac{11}{81}
B. \dfrac{13}{81}
C. \dfrac{5}{27}
D. \dfrac{17}{81}
E. \dfrac{19}{81}