A Boy Wishes to Row Across a River in the Shortest

Multiple Choice

A boy wishes to row across a river in the shortest possible time. He can row at 2 m/s in still water and the river is flowing at 1 m/s. At what angle $\theta$ should he point the bow (front) of his boat?

A) 30 $\degree$
B) 45 $\degree$
C) 60 $\degree$
D) 63 $\degree$
E) 90 $\degree$