Task: Question Answering
Input (English): 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: Two students studied the atmosphere of Earth and other planets from our solar system. Zack learned about Earth's atmosphere, while Ken learned about the atmospheric conditions on planet Venus. 
Question: Which student learned less about carbon dioxide clouds?
Output (English): Zack.