给定一段文本，计算其中单词的数量，并列出出现频率最高的5个单词。


In computer science, artificial intelligence, sometimes called machine intelligence, is intelligence demonstrated by machines, in contrast to the natural intelligence displayed by humans.
该文本中有20个单词。出现频率最高的5个单词是intelligence（2次）、machine、science和demonstrated，均出现1次。