No book can possibly explain all words, especially when they are so dissimilar as your examples. While begins clauses whereas/while unlike is usually a proposition and cnannot act as a conjunction. In contrast to is a phrase or a prepsotional idiom.
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Anonymousthe book we're using doesn't explain WHEN each is used.The lesson was obviously designed to alert the students to the meanings of these expressions so that they can recognize them passively when they see or hear them. I suspect that it's not necessary for them to know when to generate these expressions for now or the book would have said something a