10 books are placed at random in a shelf. The probability that a pair of books will always be together is -

A. $$\frac{{1}}{{2}}$$ B. $$\frac{{2}}{{5}}$$ C. $$\frac{{8}}{{15}}$$ D. $$\frac{{9}}{{20}}$$

A. $$\frac{{10}}{{21}}$$ B. $$\frac{{11}}{{21}}$$ C. $$\frac{{2}}{{7}}$$ D. $$\frac{{5}}{{7}}$$

A. $$\frac{{1}}{{3}}$$ B. $$\frac{{3}}{{4}}$$ C. $$\frac{{7}}{{19}}$$ D. $$\frac{{8}}{{21}}$$ E. $$\frac{{9}}{{21}}$$

A. $$\frac{{1}}{{6}}$$ B. $$\frac{{1}}{{8}}$$ C. $$\frac{{1}}{{9}}$$ D. $$\frac{{1}}{{12}}$$