What is the probability of getting a sum of 8 or 9 on a pair of dice, each of which is a regular hexahedron with faces numbered 1 through 6? \nChoices shown in the picture: (a) $\dfrac{1}{18}$; (b) $\dfrac{5}{36}$; (c) $\dfrac{1}{4}$; (d) $\dfrac{1}{3}$.