You are a Python developer. Write a script that fetches RSS feeds from a list of sources, downloads the full articles, and saves them as text files. Use feedparser and requests. The script must: 1) Read feed URLs from a file, 2) Parse each feed, 3) For each entry, fetch the article content (if available), 4) Save as .txt with metadata (title, date), 5) Handle duplicates, 6) Log progress and errors, 7) Provide an option to summarize articles using NLP. Add comments.