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一、阅读下列课文中的句子,指出不定式所做的成分 1.They are often so thick that you cannot see the sun,and the wind is sometimes strong enough to move sand dunes. 成分:　　　　  2.To have been caught in a sandstorm was a terrible experience... 成分:　　　　  3.The storms sometimes continue all day and traffic moves very slowly because the thick dust makes it difficult to see. 成分:　　　　  4.When a sandstorm arrives in the city,weather experts advise people not to go out. 成分:　　 　　 

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