Passage 2
　　Ever since humans have lived on the 11 , they have made use of various forms of communication. Generally, this expression of thoughts and feelings has been in the form of 12 speech. When there is a language barrier,
　　communication is "13 through sign language in which motions 14 for letters, words, and ideas. Tourists and the people unable to hear or speak have had to 15 to this form of expression. Many of these symbols of whole words are very 16 and exact and can be used 17 ; spelling, however, cannot.
　　Body language 18 ideas or thoughts by certain actions, either
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　　intentionally or unintentionally. A wink can be a way of indicating that the party is only joking. A nod signifies approval, while shaking the head indicates a 19 reaction.
　　Other forms of nonlinguistic language can be found in Braille (a system of raised dots read with the fingertips) , signal flags, Morse code, and smoke signals. Road maps and 20 signs also guide, warn, and instruct people.
　　While language is the most common form of communication, other systems and techniques also express human thoughts and feelings.

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