A、Because there is large number of vocabulary. B、Because the non-verbal languages are not easy to understand. C、Because the gram

When you learn a foreign language you must learn more than just the words and the grammar. To communicate successfully in speech, you must also learn the non-verbal language, or "body language" of that culture. Body language refers to facial expressions, gestures, and other movements of the body that send messages. This means of communication is so important that we may actually say more with our movement than we do with words.
    Speaking a foreign language is sometimes difficult because we may not understand the non-verbal signals of another culture, or they may mean something very different from what they mean in our culture. For example, in Spanish-speaking countries, children show respect to an older person by not looking directly into the person’s eyes during a conversation. In other countries, looking into a person’s eyes is expected. For example, if you don’t do it in the U.S., people may think you are afraid or angry.