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. 

Example Input: Water vapor is in warm air. The warm air cools. The warm air expands. The water vapor in the air condenses. The water vapor forms water droplets or ice crystals. 
Example Output: How are clouds formed?

Example Input: Solution caves are formed in limestone and similar rocks by the action of water. After a rain, water seeps into cracks and pores of soil and rock. The water percolates beneath the land surface. Some of the water reaches a zone where all the cracks and pores in the rock are already filled with water. Rainwater absorbs some carbon dioxide as it passes through the atmosphere and even more as it drains through soil and decaying vegetation. The water combines chemically with the carbon dioxide. A weak carbonic acid solution is formed. This acid slowly dissolves calcite, forms solution cavities, and excavates passageways. 
Example Output: Describe the process of desalination

Example Input: Dissolution of limestone forms caves. Rain gets carbon dioxide from the air. When rain goes into soil it creates an acid. The acid dissolves the limestone along cracks. Some will dissolve enough to form caves. 
Example Output:
How do caves form?