If $$a_1, a_2, a_3$$, and $$a_4$$  is the decreasing order of the elements in $$\left\{\frac{2}{7}, \frac{7}{15}, \frac{5}{8}, \frac{9}{23}\right\}$$ then $$a_1 - a_4 =$$

A

$$\frac{5}{8}$$

B

$$\frac{17}{56}$$

C

$$\frac{19}{56}$$

D

$$\frac{2}{7}$$