词汇选项
1、Social distance is not always rigidly fixed but is determined in part by the situation. When the young of apes and humans are mobile but not yet under control of the mother's voice, social distance may be the length of her reach. This is readily observed among the baboons in a zoo. When the baby approaches a certain point, the mother reaches out to seize the end of its tail and pull it back to her. When added control is needed because of danger, social distance shrinks. To show this in man, one has only to watch a family with a number of small children holding hands as they cross a busy street. The example of the children holding hands when crossing the street in the paragraph shows that _________.
A．social distance is not always needed
B．there is no social distance among small children
C．humans are different from animals in social distance
D．social distance is sometimes determined by outside factors