单项选择题

Passage Four

Ever since humans have live on the earth, they have made use of various forms of communication. Generally, this expression of thoughts and feelings has been in the form of oral speech. When there is a language barrier, communication is accomplished through sign language in which motions stand for letters, words, and ideas. Tourists and the people unable to hear or speak have had to resort to this form of expression. Many of these symbols of whole words are very vivid and exact and can be used internationally; spelling, however, cannot. Body language transmits ideas or thoughts by certain actions, either intentionally or unintentionally. A wink can be a way of indicating that the part is only joking. A nod Signifies approval, while shaking the head indicates a negative 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 picture 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.

Sign language is said to be very vivid and exact and can be used internationally except for （）

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