Final answer:
A subject directory is a curated collection of links organized by topic for easier navigation and is utilized for finding information on specific subjects, ensuring a more focused and reliable search result.
Step-by-step explanation:
A subject directory is best described by option 4: A type of search engine that only searches for information related to a specific topic. Unlike standard search engines which index the web at large, subject directories categorize websites by topics and provide a curated collection of links related to those specific subjects. They are particularly useful for academic or scholarly research since they often contain hand-picked resources evaluated for relevance and reliability.
When conducting research, it's important to choose specific key terms and be aware of the domain of a website, like .edu or .gov, to ensure trustworthy information. Furthermore, features such as Link It Up can provide a brief but essential introduction to websites that can enhance understanding of a topic. Lastly, accessing academic reading materials through library databases or recommended by faculty members can also lead to credible sources.