Many homework or test questions need only a short answer; in some cases a single sentence is enough. In such cases, you can comply with the S of UDS (Understand-Do-Show) by rephrasing the question as the subject of (the first sentence of) your answer. Here are some examples:
Question: Give one reason why Germany lost the second world war.
Answer: One reason why Germany lost the second world war is that Hitler did not trust his generals and ignored their advice.
Question: What are the main functions of a modern mobile phone?
Answer: The three main functions of a modern mobile phone are: communicating with others, taking photographs, browsing the internet.
Question: Why do young people start smoking although they know the dangers?
Answer: Topic sentence: There are three important reasons why young people start smoking, even though they know the dangers. Reason 1: One reason is that teenagers are more likely to experience peer pressure than adults. Explanation of Reason 1: Peer pressure is the pressure young people have from their friends to do risky things. They want to be popular and part of the group, so they do the same things as the rest of the group are doing. Reason 2: A second cause of smoking among young people is that they want to rebel Explanation of Reason 2: Many adolescents have strong desire to distance themselves from their parents. Reason 3: A third significant reason why young people take up smoking is that they believe it makes them look cool. Explanation of Reason 3: Self-image is extremely important at this stage in most people's lives, etc.