The speed of a swimmer in still water is 20 m/s. The speed of river water is 10 m/s and is flowing due east. If he is standing on the south bank and wishes to cross the river along the shortest path, the angle at which he should makeh is strokes w.r.t. north is given by:

A

$$0^\circ$$

B

$$60^\circ$$ west

C

$$45^\circ$$ west

D

$$30^\circ$$ west