我必须掌握它，因为我必须掌握我的生活。
协作学习是我们新课程的趋势，必须掌握它。
Cooperative Learning is the trend in our new curriculum. We should master it.
而如果你真创作了一个病毒，试验时你可千万要小心，你必须掌握它运行时的所有细节问题，否则你的系统也可能被它捣毁。
If you do create a virus, though, be careful with it. Make sure you know it is working properly or you may wipe out your own system by accident.
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