Answer:
Your friend should examine the main idea.
Step-by-step explanation:
Research is the process of looking for information or studying some topic or issue in order to answer a question or solving a situation. In most cases, when doing research it is necessary to look for other documents that provide valuable information to answer the research question. For this documents to be useful, it is necessary for them to be relevant and important for your research question, this means the documents focus on the same topic of your research and provide information that in some way answers your question or help you to understand some aspect of it better. This means you need to evaluate if the main idea, topic, and purpose of the research document are the same or it is similar to the ones of your research. Thus, if your friend is trying to know whether a source is relevant or important the first step is to determine the main idea in each source and compare it to the idea of your research as if they are similar or the same then the research is relevant.