The great deficiency of libraries, as we know them, is that while titles are catalogued, the libraries have no master indexes of the contents of books. Individual volumes, it is true, have indexes, often of inferior quality, but even the best indexes must be examined one at a time. The great advantage of the electronic library is that a computer could search and analyze its contents without proceeding volume by volume. As work in artificial intelligence develops, computer systems may also become adept at more complex tasks, such as summarizing texts, which has been accomplished experimentally.
What does the writer mainly talk about in this passage？

A. The deficiencies of the library in providing information.
B. The different applications of the computer and the library.
C. The advantages and disadvantages of the computer and library.
D. The advantages of the computer in search of information.