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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