单选题 .  Another cultural aspect of nonverbal communication is one that you might not think about: space. Every person perceives himself to have a sort of invisible shield surrounding his physical body. When someone comes too close, he feels uncomfortable. When he bumps onto someone, he feels obligated to apologize. But the size of a person's "comfort zone" depends on his cultural ethnic origin. For example, in casual conversation, many Americans stand about four feet apart. In other words, they like to keep each other "at arm's length", people in Latin or Arab cultures, in contrast, stand very close to each other, and touch each other often. If someone, from one of those cultures stands too close to an American while in conversation, the American may feel uncomfortable and back away.
    When Americans are talking, they expect others to respond to what they are saying. To Americans, polite conversationalists empathize by displaying expressions of excitement or disgust, shock or sadness. People with a "poker face", whose emotions are hidden by a deadpan expression, are looked upon with suspicion. Americans also indicate their attentiveness in a conversation by raising their eyebrows, nodding, smiling politely and maintaining good eye contact. Whereas some cultures view direct eye contact as impolite or threatening, Americans see it as a sign of genuineness and honesty. If a person doesn't look you in the eye, American might say, you should question his motives—or assume that he doesn't like you. Yet With all the concern for eye contact, Americans still consider staring—especially at strangers—to be rude.16.  What the author discussed in the previous section is most probably about ______.