Answer:
Chain stores stock mainly books of general interest, such as books by popular authors and self-help books.
Step-by-step explanation:
If Signature Books bookstore decides to invest and specialize in a particular type of books (foreign-language books and learning materials, in this case) they will be able to sell much more than if they didn't. This is because chain stores usually sell popular books such as best sellers, books of general interest, but in this stores you won't find specialized books. Therefore, investing in a particular type will push up their sales.