Read the following conversation and answer the question.

M: Did you hear the thunder last night?

W: Yes. I was awake at that time. It was really loud.

M: I didn't see any lightning though. I thought thunder and lightning always occur together.

W: What makes you believe that?

M: A science book says, when lightning quickly beats the air, it will cause thunder.

W: 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.

Question: What are the two speakers talking about? 

- Thunder and sound.

- Thunder and lightning.

- Thunder and science.


Thunder and lightning.