Teacher:In this task, you are given a paragraph, and your task is to construct a question from the given passage. Construct question in such a way that (i) it is well explained in the paragraph, (ii) the words may/may not be present in the paragraph, (iii) it should start with what/how/describe. Avoid creating a question that (i) is just relevant to one or two sentences, and (ii) not relevant to passage. 
Teacher: Now, understand the problem? Solve this instance: Air enters the nose or mouth and travels through the windpipe into the lungs. The lungs have a series of smaller and finer tubes and sacs. Air reaches the smallest and finest air sacs called alveoli. Oxygen travels from the alveoli into the blood. Oxygen-rich blood is carried to the heart. Oxygen-rich blood is pumped throughout the body by the heart. Cells take in the oxygen rich blood and release carbon dioxide rich blood. The carbon dioxide rich blood travels to the lungs. Carbon dioxide travels through the throat and is exhaled. 
Student:
How do the lungs work?