Điền số thích hợp vào ô trống:

$\dfrac{4}{5} \times \dfrac{5}{6} \times \dfrac{6}{7} \times \dfrac{7}{8} = \dfrac{a}{b}$. Khi đó:

$a=$

; $b=$

A. $\dfrac{4}{5}$

B. $\dfrac{5}{4}$

C. $\dfrac{4}{9}$

D. $\dfrac{5}{9}$

A. $\dfrac{{12}}{{16}}$

B. $\dfrac{{12}}{{18}}$

C. $\dfrac{2}{3}$

D. $\dfrac{3}{4}$

A. $\dfrac{5}{6}\,\,;\,\,\,\dfrac{2}{3}\,\,;\,\,\,\dfrac{8}{7}\,\,;\,\,\,\dfrac{1}{2}$

B. $\,\,\dfrac{8}{7}\,\,;\,\,\,\dfrac{5}{6}\,\,;\,\,\,\dfrac{2}{3}\,\,;\,\,\,\dfrac{1}{2}$   

C. $\,\,\dfrac{8}{7}\,\,;\,\,\,\dfrac{2}{3}\,\,;\,\,\,\dfrac{5}{6}\,\,;\,\,\,\dfrac{1}{2}$

D. $\,\,\dfrac{8}{7}\,\,;\,\,\,\dfrac{5}{6}\,\,;\,\,\,\dfrac{1}{2}\,\,;\,\,\,\dfrac{2}{3}\,\,$