Language acquisition is one of the central topics in cognitive science. Every theory of cognition has tried to explain it. Possessing a language is the quintessentially human trait: all common humans speak, no nonhuman ani-【M1】______ mal does. Language is main vehicle by which we know about other peoples【M2】______ thoughts, and the two must be intimately related. Every time we speak we are revealing something about language, because the facts of language【M3】______ structure are easy to come by: these data hints at a system of extraordinary【M4】______ complexity. Nonetheless, learning a first language is something every child does successfully, as a matter of a few years and without the need for formal【M5】______ lessons. With language so close to the core of what it means to be human, it is not surprising that childrens acquisition of language has received so much attention. A relating question is whether language is unique to humans. At first【M6】______ glance the answer seems obvious. Other all animals communicate with a fixed【M7】______ repertoire of symbols, or with analogue variation like the mercury in a thermometer. But nothing appears to have the combinatorial rule system of【M8】______ human language, in which symbols are changed into an unlimited set of combinations, each with a determinate meaning. On the other hand, many other claims about human uniqueness, such like that humans were the only animals【M9】______ to use tools or to fabricate them, have turned into to be false.【M10】______ 【M1】