If $$a_1, a_2, a_3, ............, a_{19}$$ are 19 arithmetic means between $$\frac{1}{4}$$ and $$-\frac{39}{4}$$ then $$a_7 =$$

A

$$-\frac{11}{4}$$

B

$$-\frac{13}{4}$$

C

$$-\frac{15}{4}$$

D

$$-\frac{17}{4}$$