Which of the following sentences contains an idiom? He said, "Dude, you need to take that money to the bank now bro before you spend it all!"

Someone stole Robin's minivan so she had to walk home from school.

The girl swore she saw a man walk up the stairs, but when she followed him he had disappeared into thin air.

The girl swore she saw a man walk up the stairs, but when she followed him he had disappeared into thin air.

Idioms are phrases, sometimes exaggerated, that are used to describe something. It doesn’t literally mean what it is describing.

The sentence contains the idiom:
“Disappeared into thin air”
Which is impossible. But it is an idiom that means the man has completely disappeared all of a sudden.

Hope this helps!