It cited statistics from the student and Exchange Visitor Program, a Department of Homeland Security unit that tracks foreigners in the US on student visas and the schools they attend.

数据援引自国土安全部中负责中学生和交流访问者项目的一个部门，这个项目跟踪外国人在美国的学生签证和学习学校的统计数据。

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They can stop a unit in its tracks.

他们可以停止在其跟踪一个单位。

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The undo engine tracks transactions and creates a single undo unit that encompasses a transaction.

复原引擎会追踪异动，并建立包含异动的单一复原单位。

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Executives were "selling consistently throughout the year because stocks were doing well and they were taking profits, " says Richard Uhl, lead business analyst for the Thomson Reuters unit that tracks insider trading.

WSJ: As Tax Hikes Loomed, Some CEOs Sold Company Stock

The problem always seems to be that the remote unit first becomes intermittent, then starts to randomly change tracks, then finally dies completely.

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