The HCF of $$\frac{12}{5}, \frac{21}{6}, \frac{9}{4}$$, and $$\frac{18}{3}$$ is:

A

$$\frac{1}{20}$$

B

$$\frac{3}{2}$$

C

$$\frac{3}{5}$$

D

$$\frac{3}{7}$$