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. 

Input: Consider Input: 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. 

Output: How do the lungs work?


Input: Consider Input: Warm, moist air moves from south to north. Cool, dry air moves from north to south. The air masses meet. The conditions that form are not stable because the air masses are so different. Winds are directed in a certain way because of how the masses interact. An updraft results. Winds start to form circular patterns in the updraft. A tornado can result. 

Output: How do tornadoes form?


Input: Consider Input: Chemicals like sulfur dioxide and nitrogen are released into the air. These substances rise into the high atmosphere. They react with water and oxygen. This creates a more acidic rain. The rain with the high acid content falls. 


Output: How does acid rain form?