Which of the following expressions shows that rational numbers are associative under multiplication?

1. $\dfrac{4}{5} \times \left(\dfrac{-6}{7} \times \dfrac{8}{9}\right) = \left(\dfrac{4}{5} \times \dfrac{-6}{7}\right) \times \dfrac{8}{9}$

2. $\dfrac{4}{5} \times \left(\dfrac{-6}{7} \times \dfrac{8}{9}\right) = \dfrac{4}{5} \times \left(\dfrac{8}{9} \times \dfrac{-6}{7}\right)$

3. $\dfrac{4}{5} \times \left(\dfrac{6}{7} \times \dfrac{8}{9}\right) = \left(\dfrac{8}{9} \times \dfrac{4}{5}\right) \times \dfrac{-6}{7}$

4. $\left(\dfrac{4}{5} \times \dfrac{-6}{7}\right) \times \dfrac{8}{9} = \left(\dfrac{-6}{7} \times \dfrac{4}{5}\right) \times \dfrac{8}{9}$

$\dfrac{-1}{4} \times \left[\dfrac{2}{5} + \left(\dfrac{-5}{6}\right)\right]$ = ?

1. $\left[\dfrac{-1}{4} \times \dfrac{2}{5}\right] + \left[\dfrac{-1}{4} \times \left(\dfrac{-5}{6}\right)\right]$

2. $\left[\dfrac{-1}{4} \times \dfrac{2}{5}\right] - \left(\dfrac{-5}{6}\right)$

3. $\dfrac{2}{5} + \left(\dfrac{-1}{4}\right) \times \left(\dfrac{-5}{6}\right)$

4. $\left[\dfrac{2}{5} + \left(\dfrac{-5}{6}\right)\right] - \dfrac{1}{4}$

What should be added to $\dfrac{-3}{4}$ to get $\dfrac{7}{6}$?

1. $\dfrac{11}{24}$

2. $\dfrac{9}{24}$

3. $\dfrac{10}{25}$

4. $\dfrac{23}{12}$

What should be subtracted from $-\dfrac{7}{8}$ so as to get $\dfrac{5}{12}$?

1. $\dfrac{31}{24}$

2. $\dfrac{8}{5}$

3. $\dfrac{-31}{24}$

4. $\dfrac{-6}{8}$