A Touch of Shadow: Challenge #2 (Part 1)

Challenge Summary: The PC must solve a puzzle before he can open a vault in the village Constable's office.

Introducing The Challenge: After the PC has defeated the giant rat, Joel takes him to the Constable's office. He explains that the current Constable was called away three days ago on official business. However, he has left some equipment for the PC in the armory. The armory is locked with a puzzle lock, but he has also left instructions on how to open it. Joel hands the PC an envelope.

The envelope contains a piece of paper that reads:

"Kail is taking his dog, a white goose and a bushel of yellow corn to market. To get there, he has to cross a river. The river can only be crossed with a boat. There is a boat on the river bank that he can use, but it is small, and he can only bring one other thing with him each time that he crosses the river. The dog, the goose and the corn cannot cross the river themselves. He cannot leave the dog alone with the goose, as the dog might attack the goose. He cannot leave the goose alone with the corn, as the goose might eat the corn. How can Kail, his dog, the goose and the bushel of corn cross the river?"

The door to the armory is made of iron. On the wall next to the door are four levers: one black, one white, one green and one yellow. All the levers are currently pointing up.