单项选择题

Ever since humans have lived 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 use this form of expressions. Many of these symbols of whole words are very vivid and exact and can be used internationally; spelling, however, cannot.
Body language transmits ideas of thoughts by certain actions, either intentionally or unintentionally. A wink can be a way of indicating that the part is only a joking. A nod signifies approval, while shaking 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.

How many nonlinguistic forms of communication are mentioned in this passage()

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