Here are the correct choices for each sentence:
1. Kai said that he wanted a new palmtop.
2. Eren told me that she wanted to study French.
3. I told them not to be stupid.
4. He told us that it was time to leave.
5. Who told you that?

Explanation:
• Use said when reporting someone’s words without mentioning the listener (e.g., “Kai said…”).
• Use told when specifying who was being spoken to (e.g., “Eren told me…”).
• Said us is incorrect; instead, use told us.