它们差不多每天都有，而且做完后隔一段时间还得再做。 。
They come every day or thereabouts, and once done they require after a certain time to be done again.
我们学习了加减法后，孩子们又在数字列上加进许多新的数字，并隔2,3个数字跳来学习跳跃计数。
After we worked on adding and subtracting my girls added more Numbers to the line and jumped by twos and threes, working on skip counting.
另一个程序，名为“湮灭”，由华盛顿大学开发，能使e - mail信息隔一段时间后变得无法读取，防止其被无限期保存。
Another program, called "Vanish," being developed at the University of Washington, makes E-mail messages unreadable after a period of time, preventing them from being stored indefinitely.
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