某人带狼、羊以及蔬菜渡河，一小船除需人划外，每次只能载一物过河。而人不在场时，狗要吃羊，羊要吃菜，问此人应如何过河？-A person with a wolf, sheep and vegetables to cross the river, a boat need not only draw people outside, each containing an object across the river only. And the person' s absence, the dog