The phase difference between the following voltage and current waves $$v = 311 \sin (100 \pi t + 30^\circ)$$ Volts $$i = 17 \sin (100 \pi t - 20^\circ)$$ Amps is

A

$$30^\circ$$

B

$$20^\circ$$

C

$$50^\circ$$

D

$$10^\circ$$