Books have always been the main tools for teaching. But a vast number of new tools have come to use in this 【S1】______ century. Take audiovisual aids for an example. 'Audiovisual' 【S2】______ means 'hearing-and-seeing'. These aids to learn include 【S3】______ films, television, audiotapes, videotapes, slides, recordings, charts, or graphs. In many schools there are language 【S4】______ laboratories where students studying foreign languages can listen to recordings of natural speakers. The students can 【S5】______ record their speech and play back tape to hear their 【S6】______ own pronunciation. Tremendous strides have been made in television instruction. Thousands of schools are now using television as part of the irregular teaching program. 【S7】______ Hundreds of closed-circuit television systems have been set in schools and colleges. There are more than 200 【S8】______ educational television stations in the United States majoring in programs of many types. For such large 【S9】______ audiences, television stations can spend more money to preparing programs than any one school could spend. 【S10】______ In television classrooms, students may see expensive scientific equipment in use. They may see close-ups of historical documents. Or they may hear talks by famous scientists or writers. 【S1】