Three jealous（妒忌的） men take their wives out for a trip. No one wanted to leave his wife with either of the other two men. Now they have to cross a river in a boat which can only take two people at a time. The men are extremely jealous and no woman will have a chance to stay together with any other man without her husband being present. How do they cross the river?

Key: A crosses the river with his wife first and he returns alone． Then B＇s and C＇s wives cross together． Then A＇s wife comes back, B and C cross over and B returns with his wife, A and B then cross and C＇s wife returns． Now A＇s and B＇s wives cross the river again． Finally C comes back to fetch his wife．