Analysis: Because you can only take one thing across the river at a time, you can only take sheep across the river for the first time, and you can take wolves or sheep for the second time, but you can't put them there, so bring the sheep back when you come back, send another one for the third time, and finally take the sheep away.

Solution: take the sheep across the river for the first time, leaving the wolf and cabbage;

The second time I crossed the river with cabbage, I left the wolf behind, but I brought the sheep back when I came back;

Take the wolf across the river for the third time, leaving the sheep;

Finally, take the sheep across the river.

A * * * must be shot four times to complete.