Which of the following numbers is in standard form?

1. $\dfrac{-12}{26}$

2. $\dfrac{-49}{70}$

3. $\dfrac{-9}{16}$

4. $\dfrac{28}{-105}$

$\left(\dfrac{-9}{16} \times \dfrac{8}{15}\right)$ = ?

1. $\dfrac{-3}{10}$

2. $\dfrac{-4}{15}$

3. $\dfrac{-9}{25}$

4. $\dfrac{-2}{5}$

$\dfrac{4}{9} \div\ ? = \dfrac{-8}{15}$

1. $\dfrac{-32}{45}$

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

3. $\dfrac{-9}{10}$

4. $\dfrac{-5}{6}$

Between any two given rational numbers we can find

1. one and only one rational number

2. only two rational numbers

3. only ten rational numbers

4. infinitely many rational numbers