You are given a background paragraph that describes one or more causal or qualitative relationships such as a relationship in economics or a scientific law and a story that makes use of the concepts or the relationship described in the provided paragraph. You are also given a question about the story that requires an understanding of the relationship described in the background paragraph and the story. You need to come up with an answer to the given question; the answer will be a span from either the question or the story. In order to correctly answer the given question, you need to understand the relationship mentioned in the background paragraph and should be able to use it to understand that in the story. Your answer can not consist of any word that is not mentioned in any of these: the background paragraph, the story, or the question. You can directly copy and paste a span from the story or the question while answering the given question.

Background Paragraph: Clouds on Earth are made of water vapor. Venus's clouds are a lot less pleasant. They are made of carbon dioxide, sulfur dioxide and large amounts of corrosive sulfuric acid! The atmosphere of Venus is so thick that the pressure on the surface of Venus is very high. In fact, it is 90 times greater than the pressure at Earth’s surface! The thick atmosphere causes a strong greenhouse effect. As a result, Venus is the hottest planet. Even though it is farther from the Sun, Venus is much hotter even than Mercury. Temperatures at the surface reach 465°C (860°F). That’s hot enough to melt lead!. 
Story: In year 2200, David is an astronaut and an avid galaxy hopper from a planet hundred light years away. He ended up in the solar system in search of water. He identified three planets, planet A, planet B and planet C. Little did he know that less than a hundred years ago people used to call planet A as Earth, planet B as Venus, and planet C as Mercury. 
Question: Would planet C be hotter or cooler than planet B?
cooler.

Background Paragraph: The lungs of mammals are unique in having alveoli . These are tiny, sac-like structures. Each alveolus is surrounded by a network of very small blood vessels (see Figure below ). Because there are millions of alveoli in each lung, they greatly increase the surface area for gas exchange between the lungs and bloodstream. Human lungs, for example, contain about 300 million alveoli. They give the lungs a total surface area for gas exchange of up to 90 square meters (968 square feet). That’s about as much surface area as one side of a volleyball court!. 
Story: Two groups of students studied Biology. Group One studied mammals, while Group Two studied birds. They focused on the respiratory system. 
Question: Which group of students learned more about alveoli?
One.

Background Paragraph: Liquid water is a fluid. The hydrogen bonds in liquid water constantly break and reform as the water molecules tumble past one another. As water cools, its molecular motion slows and the molecules move gradually closer to one another. The density of any liquid increases as its temperature decreases. For most liquids, this continues as the liquid freezes and the solid state is denser than the liquid state. However, water behaves differently. It actually reaches its highest density at about 4°C. 
Story: Mark decides he want a cold drink and puts a bottle of warm water in his freezer. By doing this he makes the water colder and as water cools its density increases eventually freezing and becoming a solid, Ice. After a while mark forgets that he put the bottle of water in the freezer. He eventually remembers and comes back to check and the bottle of water is frozen solid. Because of this he leaves the bottle out on his kitchen counter for a few hours and returns to a nice cold bottle of water. 
Question: Which is denser, warm water or ice?

ice.