Puzzles

Okay, I've been working on a list of logic puzzles for a while now, and these are the only four I can't get. Does anyone else know?

1. There are three lights in a room. Red, green and blue. There are three switches in another room, which can't be seen at the same time as the lights. Each one of the three switches is connected to a light. The lights are all turned off at the beginning (assume switches are in down position). You go to the room with the switches and turn some ON. You go to the room with the lights to see which light (or lights) went ON. You come back to the switch room and you are able to relate each light to each switch. How do you do that if you can only see the lights once? (I mean, turn some switches on, go see the lights, come back to the switches room and say: "1st switch is green, 2nd switch is blue....)

2. A man is lying dead in a field with a rock next to him. There has been no-one or nothing else in the field, how did he die?

3. There is a primitive village that has this odd custom, that when a woman cheats on her husband, she tells every man in the village about it, except for her husband. Men never talk about cheats they are aware of with each other. The custom also says that when a man realizes he's been cheated, he hangs his wife at the same night. There comes a time in the village when the priest has to leave and he announces that there have been cheats in the village. The morning after everybody can see that no woman was hung. The same goes also for the next morning. But on the third morning there were women hung. How many, and how did their husbands find out? Keep in mind that men do not talk to each other about cheats and that they are very clever.

4. A man sits in his living room reading the paper. On the front page he reads of a tragic accident in a ski resort. A woman has been killed leaving her husband devestated. The man immediatley knows it was no accident, that in fact the husband had murdered his wife. How?