The greatest value of k such that each one of the numbers $$\ \frac{4}{3k}, \frac{20}{42k},\frac{8}{6k}\ and \frac{36}{63k}\ $$is an integer is

A

$$\frac{4}{126}$$

B

$$\frac{4}{8}$$

C

$$\frac{4}{36}$$

D

$$\frac{4}{42}$$