answer: #Person1# thought thunder and lightning always occur together. #Person2# corrects #Person1# that the lightning can't be seen if it's very high in the sky.
documents: #Person1#: Did you hear the thunder last night?
  #Person2#: Yes. I was awake at that time. It was really loud.
  #Person1#: I didn't see any lightning though. I thought thunder and lightning always occur together.
  #Person2#: What makes you believe that?
  #Person1#: A science book says, when lightning quickly beats the air, it will cause thunder.
  #Person2#: I guess you didn't read the whole article because the book also says if the lightning is very high in the sky, you might not see that.