Choose the item (A, B, C or D) that best completes the unfinished statement.

Sometimes people add to what they say even when they don't talk. Gestures are the "silent language" of every culture. We point a finger or move another part of the body to show what we want to say. It is important to know the body language of every country or we may be misunderstood. In the United States, people greet each other with a handshake in a formal introduction. The handshake must be firm. If the handshake is weak, it is a sign of weakness or unfriendliness. Friends may place a hand on the other's arm or shoulder. Some people, usually women, greet a friend with a hug.

Space is important to Americans. When two people talk to each other, they usually stand about two and a half feet away and at an angle, so they are not facing each other directly. Americans get uncomfortable when a person stands too close. They will move back to have their space. If Americans touch another person by accident, they say, "Pardon me." or "Excuse me." Americans like to look the other person in the eyes when they are talking. If you don't do so, it means you are bored, hiding something, or are not interested. But when you are stare at someone, it is not polite. For Americans, thumbs-up means yes, very good, or well done. Thumbs down means the opposite. To call a waiter, raise one hand to head level or above. To show you want the check, make a movement with your hands as if you are signing a piece of paper. It is all right to point at things but not at people with the hand and index finger. Americans shake their index finger at children when they scold them and pat them on the head when they admire them. Learning a culture's body language is sometimes confusing. If you don't know what to do, the safest thing to do is to smile

The word “them” in paragraph 2 refers to