单选题 .  Ever since humans lived on the earth, they have made use of     41    forms of communication. Generally this     42    of thoughts and feelings     43    been in the form of oral speech.     44    there is a language barrier, communication is     45    through sign language     46    motions stand for letters, words, and     47    .
    Tourists and people     48    to hear or speak have had to     49    to this form of expression. Many of these symbols of whole words are very vivid and     50    and can be used internationally; spelling     51    , cannot.
    Body language     52    ideas or thoughts     53    certain actions, either intentionally     54    unintentionally. A wink can be a way of     55    that the party is only joking. A nod signifies approval,     56    shaking the head indicating a     57    reaction.
    Other forms of nonlinguistic language can be     58    in Braille (a system of     59    dots read with the fingertips), signal flags, Morse code, and smoke signals. Road, maps and picture signs also guide, warn, and instruct people. While     60    is the most important form of communication, other systems and techniques also express human thoughts and feelings.41.