People thinking about the origin of language for the first time usually arrive at the conclusion that it developed gradually as a system of grunts, hisses and cries and     1    a very simple affair in the beginning.     2    , when we observe the language behavior of     3    we regard as primitive cultures, we find it     4    complicated. It was believed that an Eskimo must have the tip of his tongue a vocabulary of more than 10,000 words     5    to get along reasonably well, much larger than the active vocabulary of an average businessman who speaks English.     6    , these Eskimo words are far more highly inflected than     7    of any of the well-known European languages, for a     8    noun can be spoken or written in     9    hundred different forms, each     10    a precise meaning different from that of any other. The forms of the verbs are even more     11    . The Eskimo language is, therefore, one of the most difficult in the world to learn,     12    the result that almost no traders or explorers have     13    tried to learn it. Consequently, there has grown up, in communication between Eskimos and whites, a jargon     14    to the pidgin English used in Old China, with a vocabulary of from 300 to 600 uninflected words. Most of them are derived from Eskimo but some are derived from English, Danish, Spanish, Hawaiian and other languages. It is this jargon that is usually     15    by travelers as "the Eskimo language". 
 
【正确答案】 D
【答案解析】 这句话是说“第一次考虑到语言的起源问题时,人们都会认为语言是从人们的咕哝、喊叫逐渐发展起来的,并且开始肯定是很简单的”。must have+过去分词,表示对过去事情的猜测。