A. With a listening typewriter, what an author says would be automatically recognized and displayed in front of him or her. However, speech recognition is not yet advanced enough to provide people with a reliable listening typewriter.B. An aim of our experiments was to determine if an imperfect listening typewriter would be useful for composing letters.C. Participants dictated letters, either in isolated words or in consecutive word speech. They did this with simulations of listening typewriters that recognized either a limited vocabulary or an unlimited vocabulary.D. Results indicated that some versions, even upon first using them, were at least as good as traditional methods of handwriting and dictating.E. Isolated word speech with large vocabularies may provide the basis for a useful listening typewriter.上述摘要中，哪一段为“背景”介绍？