But prolonged viewing may result in an aching head, according to Dr Michael Rosenberg, an ophthalmology professor at Northwestern University Feinberg School of Medicine in Chicago.

但芝加哥西北大学费恩柏格医学院的眼科学教授迈克尔·罗森堡博士说，长时间观看3d电影可能会导致头痛。

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Records of those who paid the head tax are still available for viewing in the National Archives of Canada.

那些交了人头税的人，其档案至今还可以在加拿大国家档案馆查阅到。

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A head tax was also imposed. Records of those who paid the head tax are still available for viewing in the National Archives of Canada.

那些交了人头税的人，其档案至今还可以在加拿大国家档案馆查阅到。

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This will certainly make you want to head for your own viewing spot to watch the sunset.

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They also tested whether the learning process was conscious by distracting the subjects during the video viewing - the volunteers were asked to do simple arithmetic sums in their head, for example.

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Vodafone is also running several pilots, says Richard Saggers, the head of its mobile advertising unit, in which subscribers receive free content in exchange for viewing ads.

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