Boom boom!( I'm here, come to me!) Krak krak!( Watch out, aleopard  !) Hok hok hok!( Hey, crowned eagle!) Very good -- you've already mastered half the basic vocabulary of the Campbell's monkey, which lives in the forests of the Tai National Park in Ivory Coast. The adult males have six types of call, each with a specific meaning, but they can mix two or more calls together into a message with a different meaning. Having spent months recording the monkeys' calls in response to both natural and artificialstimuli , a group led by Klaus Zuberbuhler of the University of St. Andrews in Scotland argues that the Campbell's monkeys have a certain form ofsyntax . This is likely to be controversial because despite great effort to teachchimpanzees  language, they showed little or no ability to combine the sounds they learned into a sentence with a larger meaning. Syntax, basic to the structure of language, uniquely belongs to humans. "Krak" is a call that warns of leopards in the neighborhood. The monkeys give it in response to real leopards and to leopard shouting broadcast by the researchers. The monkeys can vary the call by adding "-oo": "Krak-oo" seems to be a general word for hunter, but one given in a special context - when monkeys hear but don't see a hunter, or when they hear the alarm calls of another species. The "boom-boom" call invites other monkeys to come toward the male making the sound. Two booms can be combined with a series of "krak-oos", with a meaning entirely different to that of either of its single parts. "Boom boom krak-oo krak-oo krak-oo" is the monkey's version of "Timber!" - it warns of falling trees. If Zuberbuhler is correct, the Campbell's monkeys can both vary the meaning of specific calls by adding something and combine calls to make a different meaning. According to the passage, it seems that  _  .
Zuberbuhler has spent years in the forests the writer isn't sure of Zuberbuhler's opinions the Campbell's monkeys are cleverer than other animals the Campbell's monkeys can express six meanings by calls