Assume every 7-digit whole number is a possible telephone number except those which begin with 0 or 1 . What fraction of telephone numbers begin with 9 and end with 0 ?
Answer Choices
A. \dfrac{1}{63}
B. \div \dfrac{1}{80}
C. \dfrac{1}{81}
D. \dfrac{1}{90}
E. \dfrac{1}{100}