Why did Ren go to the dentist? (have/a toothache)
He went to dentist because he had a toothache.
Ask a question (Why / you / ....?)
Why did you eat a hamburger?
Why did he drink water? (thirsty)
He drank water because he was thirsty.
Why didn't she play outside? (raining)
She didn't play outside because it was raining.
Ask a question (Why / you / .....?)
Why did you brush your teeth?
Why didn't Mike play basketball? (break)
Mike didn't play basketball because he broke his leg.
Why did he take a shower? (dirty)
He took a shower because he was dirty.