On circle O, points C and D are on the same side of diameter \overline{A B}, \angle A O C=30^{\circ}, and \angle D O B=45^{\circ}. What is the ratio of the area of the smaller sector C O D to the area of the circle? B
Answer Choices
A. \dfrac{2}{9}
B. \dfrac{1}{4}
C. \dfrac{5}{18}
D. \dfrac{7}{24}
E. \dfrac{3}{10}