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: The air is cold. Water is in the air. The water forms tiny ice crystals. The ice crystals collide with each other. The ice crystals stick to each other. The ice crystals get bigger as more of them stick together. The ice crystals get too heavy to be in the air. The ice crystals become snowflakes. The snow flakes fall to the ground as snow. 
Example Output: How does snow form?

Example Input: A sperm meets an egg in the uterus of a woman. The sperm implants itself into the egg. The sperm and egg form a zygote on the wall of the uterus. The fetus grows and develops. The woman gives birth to a baby. The baby is raised by parents until it is able to take care of itself. The person goes out into the world and finds a job. The person meets other people and has a life. The person gets a career, and gets married. The person retires and eventually passes away. 
Example Output: Describe the life cycle of a human

Example Input: People breathe and expel carbon dioxide. Engines produce carbon dioxide. Living things produce waste. Waste decomposes. Decomposition produces methane. Water evaporates. Water vapor joins the atmosphere. Carbon dioxide, water vapor and methane are greenhouse gases. 
Example Output:
How do greenhouse gases form?