19. (1985 American High School Mathematics Examination) In a mixed class of boys and girls, a student is selected to represent the class, with each student having an equal chance of being selected, and the probability of a boy being selected is $\frac{2}{3}$ of the probability of a girl being selected. Then the ratio of the number of boys to the total number of students in the class is ( ).
A. $\frac{1}{3}$
B. $\frac{2}{5}$
C. $\frac{1}{2}$
D. $\frac{3}{5}$
E. $\frac{2}{3}$