Dr. Simonson was trying to explain to Justine why her smoking might lead to further health problems. He took out a model of a lung and showed her the air passages and windpipe. He then explained how smoking affected the lung and that she may be susceptible for lung cancer.

What was the role of the lung model in this scenario?

It was used to understand something that cannot easily be seen.
It was used to prove that smoking causes health problems.
It was used to demonstrate a pattern.
It was used to represent something big.