A、External noise. B、Physiological noise. C、The effect of a cold. D、Psychological effect. B

There are three types of noise that can block communication. The first, external noise includes those obvious things that make it difficult to hear, as well as many other kinds of distractions. For instance, too much cigarette smoke in a crowded room might make it hard for you to pay attention to another person, and sitting in the rear of an auditorium might make a speaker’s remarks unclear. External noise can interrupt communication almost anywhere in our model -- in the sender, channel, message, or receiver.
    The second type of noise is physiological. A hearing disorder is probably the most obvious type of physiological barrier, although many more exist. Consider, for instance, the difficulty you experience as a listener when you are suffering from a cold or are very tired. In the same way you might speak less when you have a sore throat or a headache.
    Psychological noise refers to forces within the sender or receiver that make these people less able to express or understand the message clearly. For instance, a fisherman might exaggerate the size and number of fish caught in order to convince himself and others of his talents. In the same way, a student might become so upset upon learning that she failed a test that she would be unable to clearly understand where she went wrong.