Which of the following is a proper fraction:

$\frac{19}{18}, \frac{18}{11}, \frac{5}{7}, \frac{13}{8}, \frac{9}{5}, \frac{22}{20}, \frac{33}{13}$

For proper fractions, the numerator should be less than the denominator.

Among the given fractions all of them have numerators greater than denominators except $\frac{5}{7}$, where numerator 5 is less than denominator 7.

Thus,$\frac{5}{7}$ is a proper fraction.