题目内容：
Decide which of the choices given below would best complete the passage if inserted in the corresponding blanks. Mark the best choice for each blank on your answer sheet.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(31)__________ a very simple affair(32)__________ (33)_________, when we observe the language behaviour of (34).__________ we regard as primitive cultures we find it (35)_________ complicated. It was believed that an Eskimo must have at the tip of his tongue a vocabulary of more than 10,000 words (36)_________to get along reasonablywell,muchlarger thanthe(37)__________ vocabulary of an average businessman who speaks English.(38)these Eskimo words are far more highly inflected (词尾变化的) than (39)_________ of any of the well-known European languages, for a (40)__________ noun can be spoken or written in(41)hundred different forms, each(42)__________ a precise meaning different from(43)_________ of any other. The forms of the verbs are even more (44) _________ The Eskimo language is, (45)_________ , one of the most difficult in the world to learn,(46).__________ the result that almost no traders or explorers have(47)__________ tried to learn it.(48) _________ , there has grown up, in communication between Eskimos and whites, a jargon(49)_________ 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 jargonthat is usually(50)__________ by travellers as "the Eskimo language".根据以上资料回答下列第题： A．must be
B．must have been
C．ought to be
D．should be
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