A Boy Wishes to Cross a River in the Shortest $\theta$

Multiple Choice

A boy wishes to cross a river in the shortest possible time, without necessarily landing directly across from his starting point.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 °
B) 45 °
C) 60 °
D) 63 °
E) 90 °