The greatest fraction among the following is:

Given:
Fractions $\frac{2}{10}, \frac{3}{5}, \frac{14}{30}, \frac{4}{6}$

To find:
the greatest fraction

Calculations:
Converting the fractions to common denominator $30$, we get

$\frac{6}{30},\frac{18}{30},\frac{14}{30},\frac{20}{30}$

$\Rightarrow \frac{20}{30} =\frac{4}{6}$ is the greatest among them.

Hence, option D is the correct answer.