A good answer to a source question is made up of three parts: context, content and usefulness.For the context, look at where the source came from and who wrote it. Make sure you don't just state what it has already told you, but analyse what this means for the usefulness of the source. For example, if it's a speech by the President of the US, it probably won't mention any weaknesses. State that this weakens the usefulness of the source.For the content, try and work out what the source is trying to say overall. See what it tells you and then use your subject knowledge to find what it is missing. If it doesn't mention key points about the subject, state what it is specifically missing and then why this means the source isn't very useful. For the usefulness, essentially write a mini conclusion. State whether the source is or isn't useful in discussing the topic, and remember to put why.A tip for this one is to use three different-colour highlighters for each of these points. Take a few minutes to read through the source and highlight what you're going to say for each of these sections - it'll help the clarity of your answer when you come to write it!