(Based on a typical passage about the value of reading) The term "master-spirit" used in the context of books typically refers to individuals with extraordinary intellectual or creative power whose thoughts and influence are preserved in their writings. These are the great authors or thinkers whose works fill a library or bookcase. Option A, "a prominent writer," best fits this meaning. The passage likely refers to the books containing the "spirits" (minds, ideas, influences) of such writers.